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/guimain.py

@@ -83,7 +83,7 @@ class GuiMain(QMainWindow):
         # ============
 
         # Core Classes and Settings
-        self.theTheme    = GuiTheme(self)
+        self.theTheme    = GuiTheme()
         self.theProject  = NWProject(self)
         self.theIndex    = NWIndex(self.theProject)
         self.hasProject  = False