Update and reorganise themes (#893)

* Drop the subfolders for GUI themes
* Remove bundled font support
* Add safe file read function
* Allow loading themes from multiple locations
* Clean up unused variables
* Clean up icons class
* Merge icon theme icons
* Update icon theme class
* Remove guiDark config setting
* Fix tests
* Fix handling of default theme
* Update icon readmes
* Add test for getGuiItem common function

novelwriter/assets/icons/typicons_light/icons.conf

@@ -7,57 +7,70 @@
 ##
 
 [Main]
-name           = Typicons Light
-description    = Colourised icons for light GUI theme based on Typicons.
-author         = Veronica Berglyd Olsen (adaptation)
-credit         = Stephen Hutchings (icon design)
-url            = https://github.com/stephenhutchings/typicons.font
-license        = CC BY-SA 4.0
-licenseurl     = https://creativecommons.org/licenses/by-sa/4.0/
+name        = Typicons Light
+description = Colourised icons for light GUI theme based on Typicons.
+author      = Veronica Berglyd Olsen (adaptation)
+credit      = Stephen Hutchings (icon design)
+url         = https://github.com/stephenhutchings/typicons.font
+license     = CC BY-SA 4.0
+licenseurl  = https://creativecommons.org/licenses/by-sa/4.0/
 
 [Map]
-cls_none       = cancel.svg
-cls_novel      = book.svg
-cls_plot       = puzzle.svg
-cls_character  = user.svg
-cls_world      = location.svg
-cls_timeline   = calendar.svg
-cls_object     = key.svg
-cls_entity     = flag.svg
-cls_custom     = star.svg
-cls_archive    = delete.svg
-cls_trash      = trash.svg
-proj_document  = document-text.svg
-proj_title     = document-title.svg
-proj_chapter   = document-chapter.svg
-proj_scene     = document-scene.svg
-proj_note      = document-note.svg
-proj_folder    = folder.svg
-doc_h0         = heading0.svg
-doc_h1         = heading1.svg
-doc_h2         = heading2.svg
-doc_h3         = heading3.svg
-doc_h4         = heading4.svg
-delete         = delete.svg
-add            = plus.svg
-remove         = minus.svg
-close          = times.svg
-refresh        = refresh.svg
-maximise       = arrow-maximise.svg
-minimise       = arrow-minimise.svg
-done           = input-checked.svg
-search         = search.svg
-search-replace = search-replace.svg
-clear          = backspace.svg
-save           = download.svg
-edit           = pencil.svg
-check          = tick.svg
-cross          = times.svg
-hash           = hash.svg
-reference      = at.svg
-backward       = chevron-left.svg
-forward        = chevron-right.svg
-sticky-on      = pin.svg
-sticky-off     = pin-outline.svg
-bullet-on      = media-record.svg
-bullet-off     = media-record-outline.svg
+add             = typ_plus.svg
+backward        = typ_chevron-left.svg
+bullet-off      = typ_media-record-outline.svg
+bullet-on       = typ_media-record.svg
+check           = typ_tick.svg
+clear           = typ_backspace.svg
+close           = typ_times.svg
+cls_archive     = typ_delete.svg
+cls_character   = typ_user.svg
+cls_custom      = typ_star.svg
+cls_entity      = typ_flag.svg
+cls_none        = typ_cancel.svg
+cls_novel       = typ_book.svg
+cls_object      = typ_key.svg
+cls_plot        = typ_puzzle.svg
+cls_timeline    = typ_calendar.svg
+cls_trash       = typ_trash.svg
+cls_world       = typ_location.svg
+cross           = typ_times.svg
+delete          = typ_delete.svg
+doc_h0          = mixed_heading0.svg
+doc_h1          = mixed_heading1.svg
+doc_h2          = mixed_heading2.svg
+doc_h3          = mixed_heading3.svg
+doc_h4          = mixed_heading4.svg
+done            = typ_input-checked.svg
+edit            = typ_pencil.svg
+forward         = typ_chevron-right.svg
+hash            = typ_hash.svg
+maximise        = typ_arrow-maximise.svg
+minimise        = typ_arrow-minimise.svg
+proj_chapter    = mixed_document-chapter.svg
+proj_document   = typ_document-text.svg
+proj_folder     = typ_folder.svg
+proj_note       = mixed_document-note.svg
+proj_scene      = mixed_document-scene.svg
+proj_title      = mixed_document-title.svg
+reference       = typ_at.svg
+refresh         = typ_refresh.svg
+remove          = typ_minus.svg
+save            = typ_download.svg
+search          = typ_search.svg
+search_cancel   = typ_cancel-grey.svg
+search_case     = nw_search-case.svg
+search_loop     = typ_arrow-repeat-grey.svg
+search_preserve = nw_search-preserve.svg
+search_project  = typ_arrow-down-thick-grey.svg
+search_regex    = nw_search-regex.svg
+search_replace  = mixed_search-replace.svg
+search_word     = nw_search-word.svg
+settings        = typ_cog.svg
+status_idle     = typ_media-pause-grey.svg
+status_lang     = typ_globe-grey.svg
+status_lines    = typ_th-list-grey.svg
+status_stats    = typ_chart-bar-grey.svg
+status_time     = typ_stopwatch-grey.svg
+sticky-off      = typ_pin-outline.svg
+sticky-on       = typ_pin.svg