Extension Pack for Nevolution

Prepare for new features

Add following features to Nevolution:

* Better status-bar notification icon compatibility on Android pre-6.0.
* Seamless experience without any notification loss when Nevolution is being upgraded.
* No notification loss if Nevolution is crashed in any case.
* More to come...

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Main app of Nevolution: play.google.com/store/apps/details?id=com.oasisfeng.nevo