Added a way to select target calendar for adding journeys.
Updated translations.
Retrieve list of calendars in a separate thread.

Getting a list of calendars can take some time (at least on Harmattan).
This can cause a significant delay (up to 10 seconds) and UI freeze
between pressing settings icon and showing a Setting page. Running
retrieval in a separate thread allows to show Setting page immediately and
populate list of calendars later without causing UI freeze.

Also updated translations (1 more string).
[Sym] Forgot that some platforms don't support Qt Concurrent.

Symbian, in this case. Luckily, retrieving calendar list on this platform
from the main thread doesn't cause noticable delay and/or UI freeze.