* use cert4android instead of MemorizingTrustManager
* new app setting: distrust system certificates
* add network security config to manifest so that user-installed CAs will be accepted in Android 7 again
* update gradle
We can't use a repository version because there's no release yet which
contains rev. 1652769. However, this revision is necessary to get SNI with Android <4.2, too.
To avoid packaging a pre-compiled jar, this source lib has been added as a subproject:
apache-httpclient, branch 4.3.5-android, revision 1652769
Fixes#491.
* new Settings activity
* Settings: display/change user name, password, preemptive auth.
* Settings: display/change sync. interval for contacts and calendars
* requires permission GET_ACCOUNTS to list accounts in Settings
* requires permission READ_SYNC_SETTINGS to display current sync intervals
* remove obsolete files from res/
* update copyright notices
* version bump to 0.7
* moved all dependencies to gradle instead of shipping .jar files in the app/lib directory
* switched to official Android port of HttpClient instead of httpclientandroidlib
* new .gitignore and project files
