Move the landing page to IM application and remove the depency of com.android.im...

Move the landing page to IM application and remove the depency of com.android.im.plugin.jar

Some other tiny changes:
  - Allows the client to delete providersettings records through uri "content://im/providerSettings/#"
  - Allows the client to get account.keep_signed_in when query the active account with given provider.