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_dark/README.md

@@ -1,5 +1,29 @@
-## Typicons
+# Typicons for Dark Backgrounds
+
+This theme is based on Typicons. All files are prefixed, depending on whether they are based
+directly on original Typicons, redesigned, or designed from scratch.
+
+## Typicons Icons
+
+The files have a `typ_` prefix. These are colourised and rescaled Typicons, but with no other
+modifications.
 
 Copyright: Stephen Hutchings  
 Source: https://github.com/stephenhutchings/typicons.font  
 License: [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/)  
+
+## Original Icons
+
+The files have a `nw_` prefix. These are made completely from scratch for novelWriter and are not
+using any design elements from Typicons.
+
+Copyright: Veronica Berglyd Olsen  
+License: [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/)  
+
+## Mixed Icons
+
+The files have a `mixed_` prefix. These are redesigned from Typicons components, modified from
+Typicons, or consist of a mix of Typicons and new elements.
+
+Copyright: Stephen Hutchings, Veronica Berglyd Olsen  
+License: [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/)