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.conf

@@ -0,0 +1,45 @@
+##
+# Theme:  Tomorrow
+# Source: https://github.com/chriskempson/tomorrow-theme
+# Credit: Chris Kempson
+##
+# Colours:
+# Background   = ffffff : 255, 255, 255
+# Current Line = efefef : 239, 239, 239
+# Selection    = d6d6d6 : 214, 214, 214
+# Foreground   = 4d4d4c :  77,  77,  76
+# Comment      = 8e908c : 142, 144, 140
+# Red          = c82829 : 240,  40,  41
+# Orange       = f5871f : 245, 135,  31
+# Yellow       = eab700 : 234, 183,   0
+# Green        = 718c00 : 113, 140,   0
+# Aqua         = 3e999f :  62, 153, 159
+# Blue         = 4271ae :  66, 113, 174
+# Purple       = 8959a8 : 137,  89, 168
+##
+
+[Main]
+name       = Tomorrow
+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     = 255, 255, 255
+text           =  77,  77,  76
+link           =  66, 113, 174
+headertext     =  66, 113, 174
+headertag      =  66, 113, 174
+emphasis       = 245, 135,  31
+straightquotes = 240,  40,  41
+doublequotes   = 113, 140,   0
+singlequotes   = 234, 183,   0
+hidden         = 142, 144, 140
+keyword        = 240,  40,  41
+value          = 137,  89, 168
+spellcheckline = 240,  40,  41
+errorline      = 113, 140,   0
+replacetag     =  62, 153, 159
+modifier       = 245, 135,  31