[callstate] Add callstate plugin so call state can be accessed

To properly handle notifications during calls, the call state
plugin is needed to monitor current call state. Added callstate
to optional plugins list in default ngfd.ini.

Signed-off-by: Kalle Jokiniemi <kalle.jokiniemi@jollamobile.com>
[ffmemless] Don't vibrate if a call is ongoing.

Getting an calendar alarm vibration or an incoming call vibration
during a voice call can be hugely disturbing. Check call state and
don't vibrate if a call is active.

Signed-off-by: Kalle Jokiniemi <kalle.jokiniemi@jollamobile.com>
Merge pull request #30 from kjokinie/master

Add proper call state handling for vibra.