'Currently running' app drawer tab replacement

[TrianguloY]

The currently running app drawer tab showed the list of currently running apps. This feature was broken after Android 5.

The PR #6 remove it.

This is the issue mentioned in one of its comments:

Maybe by using the new UsageStatsManager it can be repurposed to a 'recently running apps'. Note that a 'recently launched apps' does exists, but it only uses the number of times the app was launched from the launcher, which is not ideal. In any case, this will be a new mode with different code, so I'll create an issue to record it but still merge this PR.