Support HTTP(S) proxies (closes #232)
Make server URL, user name and password horizontally scrollable (fixes
#241)
Debug settings

* preference screen for debug settings
* allow to disable HTTP compression
* verbose network logging only when activated
* single HttpClient for all threads (before: single HttpClient per adapter)
* bump version to 0.5.13-alpha
Debugging improvements

* force debugging options for resource detection (because there's no way to turn them on until there's an account)
* provide "report issue" button in debug settings
* provide CONTRIBUTING.md, including instructions on how to report issues
* increase socket timeout from 20 to 45 seconds (hopefully fixes #237)
* previous commit: increase total simultaneous connections to 3 (2 per host)
Ignore crappy unknown properties with illegal syntax (see issue #118)
Better invalid VCard handling

* ignore unknown properties which have invalid syntax instead of crashing
* log validation warnings for created VCards
* add VCard tests
Merge upstream
Fix #6: Tasks state doesn't get synced