Implementation of interface (template) for all modules

- Correct setup of logging
- all inkycal-modules inherit from the given template
- Added basic, optional validation
- more code cleanups
- fixed a few minor bugs

inkycal/config/__init__.py

@@ -1,4 +1,2 @@
 from .settings_parser import settings
-print('loaded settings')
 from .layout import layout
-print('loaded layout')