Added test for main preferences and improved the Preferences dialog a bit

tests/reference/prefs_novelwriter.conf

@@ -0,0 +1,69 @@
+[Main]
+timestamp = 2020-06-29 17:34:15
+theme = default
+syntax = default_light
+icons = typicons_colour_light
+guidark = True
+guifont = Cantarell
+guifontsize = 12
+
+[Sizes]
+geometry = 1100, 650
+treecols = 120, 30, 50
+projcols = 140, 55, 140
+mainpane = 300, 800
+docpane = 400, 400
+viewpane = 500, 150
+outlinepane = 500, 150
+fullscreen = False
+
+[Project]
+autosaveproject = 40
+autosavedoc = 20
+
+[Editor]
+textfont = Cantarell
+textsize = 13
+fixedwidth = False
+width = 700
+margin = 45
+tabwidth = 45
+focuswidth = 900
+hidefocusfooter = True
+justify = False
+autoselect = False
+autoreplace = False
+repsquotes = True
+repdquotes = True
+repdash = True
+repdots = True
+fmtsinglequote = ‘, ’
+fmtdoublequote = “, ”
+spelltool = internal
+spellcheck = en
+showtabsnspaces = True
+showlineendings = True
+bigdoclimit = 500
+showfullpath = False
+highlightquotes = False
+highlightemph = False
+
+[Backup]
+backuppath = 
+backuponclose = True
+askbeforebackup = True
+
+[State]
+showrefpanel = False
+viewcomments = True
+viewsynopsis = True
+searchcase = False
+searchword = False
+searchregex = False
+searchloop = False
+searchnextfile = False
+searchmatchcap = False
+
+[Path]
+lastpath = 
+