make khal work with different encodings

you can now set the encoding your terminal uses in khal.conf and all
output should be encoded with that encoding. There is also a new option
`unicode_symbols` (by default set to True), which, if disabled, makes
khal not use any fancy unicode symbols.

ikhal still doesn't respect any of these new settings (but keeps using
utf-8 for now). Alse khal --new might no work yet properly with
decodings other than utf-8.
ikhal: started to work on a calendar chooser

this should enable moving an event between different calendars
no need to try this out, it's not working yet
ikhal: moving events to other cals should work
Don't show deleted events anymore
ikhal editor: bugfixes

ikhal does not exit on pressing 'esc' in event editor anymore, but
instead returns to the default view if the event has not been edited
yet, and does nothing otherwise (will be changed). Might have fixed a
bug in editing location and description properties, but I'm too lazy to
revert to the last commit just to check.
new post
Merge remote-tracking branch 'upstream/master'
Well commit again now that I remembered to fetch/merge upstream