MH2 | Implement ScopeWakelock ctor and dtor

Put the ScopedWakelock class into its own header and its implementation
into its own cpp. Implement the refcounting of the wakelocks. However,
do not incorporate the wakelock handling into post events in halproxy
yet.

Bug: 136511617
Test: No new tests yet. Will add more in a later patchset once more
fleshed out and integrated with postEvents.
Change-Id: I0815c6a6659ec5933b799294956595b11e7bf1b3