[AndroidManifest] now uses android sdk version 20
[PreferencesHelper] Code Cleanup: fixed lint warning
[PreferencesHelper] now writes in the background
[libphonenumber] updated to version 6.2
[SimlarService] now checkNetworkConnectivityAndRefreshRegisters aborts if there is now linphone thread
Merge pull request #149 from simlar/code-cleanup-preferences-helper-libphonenumber-and-more-pullrequest

Code Cleanup Pull Request: PreferencesHelper, libphonenumber and more