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/syntax/tomorrow_night_eighties.conf

@@ -0,0 +1,45 @@
+##
+# Theme:  Tomorrow Night Eighties
+# Source: https://github.com/chriskempson/tomorrow-theme
+# Credit: Chris Kempson
+##
+# Colours:
+# Background   = 2d2d2d :  45,  45,  45
+# Current Line = 393939 :  57,  57,  57
+# Selection    = 515151 :  81,  81,  81
+# Foreground   = cccccc : 204, 204, 204
+# Comment      = 999999 : 153, 153, 153
+# Red          = f2777a : 242, 119, 122
+# Orange       = f99157 : 249, 145,  57
+# Yellow       = ffcc66 : 255, 204, 102
+# Green        = 99cc99 : 153, 204, 153
+# Aqua         = 66cccc : 102, 204, 204
+# Blue         = 6699cc : 102, 153, 204
+# Purple       = cc99cc : 204, 153, 204
+##
+
+[Main]
+name       = Tomorrow Night Eighties
+author     = Veronica Berglyd Olsen (adaptation)
+credit     = Chris Kempson (color theme)
+url        = https://github.com/chriskempson/tomorrow-theme
+license    = MIT License
+licenseurl = https://github.com/chriskempson/tomorrow-theme/blob/master/LICENSE.md
+
+[Syntax]
+background     =  45,  45,  45
+text           = 204, 204, 204
+link           = 102, 153, 204
+headertext     = 102, 153, 204
+headertag      = 102, 153, 204
+emphasis       = 249, 145,  57
+straightquotes = 242, 119, 122
+doublequotes   = 153, 204, 153
+singlequotes   = 255, 204, 102
+hidden         = 153, 153, 153
+keyword        = 242, 119, 122
+value          = 204, 153, 204
+spellcheckline = 242, 119, 122
+errorline      = 153, 204, 153
+replacetag     = 102, 204, 204
+modifier       = 249, 145,  57