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/modules/__init__.py

@@ -0,0 +1,4 @@
+##from .inkycal_agenda import agenda
+##from .inkycal_calendar import calendar
+##from .inkycal_weather import weather
+##from .inkycal_rss import rss