Notification API

* move common plugin functionality to new randomhost\Icinga\Base class
* move run() method definition to new common plugin interface randomhost\Icinga\Plugin
* replace randomhost\Icinga\Check::SERVICE_STATE_* constants with randomhost\Icinga\Plugin::STATE_* constants
* add third party NmaApi class for sending push notifications to Android devices
* add randomhost\Icinga\Notifications\Base class for notification plugins
* add randomhost\Icinga\Notifications\NotifyMyAndroid class for Android push notifications
* add randomhost\Icinga\Notifications\Smstrade class for SMS notifications