As requested in #736, this adds an entry in the settings menu that allows to blacklist certain calendars.
To avoid confusion, all the former blacklist methods and fields have been renamed to apps_blacklist. The new entries are called calendars_blacklist.
Importing the settings has not been tested with the current changes.
Closes#736
Future improvements TODO: The new setting lives in the Pebble section, i believe in the future the blackslist functionality should be centralized and put in the sidebar.
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