Collection of fixes for bugs and visual tweaks throughout Kalendar

This MR contains a number of fixes for bugs in Kalendar. In no particular order:

• Fixed bug where some incidences were covered up by others on the month view
• Fixed vertical spacing in month view -- events now always go top to bottom, all-day events first
• Added horizontal and vertical padding to lines in month view
• Calendar colours are now properly pulled from Akonadi (requires user-set colours), will then try to pull from KOrganizer config if available
• Calendar colours now visible in calendar settings
• Improved colouring of current month incidence lines in month view and schedule view, with specific adjustments for dark mode
• Incidence lines in months not current now no longer have backgrounds, just coloured text
• Double clicking on square in month view grid now correctly sets incidence editor to this date

Images:

Light mode comparison (before top, after bottom):

Dark mode comparison (before top, after bottom):

Calendar colour sync and calendar settings: