[buteo-sync-plugin-caldav] Fix QUrl creating from percent encoded strings

Calendar urls are currently saved in percent encoded format
when passed them in this format to QUrl::setPath a recoding
can happen(Tolerant mode is the default) breaking the original
server path, so we decode them first.
Merge pull request #27 from nemomobile/calendarNames

[buteo-sync-plugin-caldav] Fix QUrl creating from percent encoded string...