Automatic contact discovery and more

- Automatic contact discovery, as described [here](https://github.com/open-keychain/open-keychain/wiki/Google-Summer-of-Code-2014#automatic-contact-discovery), using first key server in list and lacking any configuration
- Integration of OpenKeychain into Android's contact app, as described [here](https://github.com/open-keychain/open-keychain/wiki/Google-Summer-of-Code-2014#integration-of-openkeychain-into-androids-contact-app), changes are not synced, newly added keys are synced when android decides to, not directly after OpenKeychain changes, causing desync
+ more fixes and changes here and there

Note: Contact sync features in both directions are disabled by default, but can be enabled in system settings -> select OpenKeychain (in accounts section) -> tick "Contacts"
Please use Constants.TAG everywhere :)