Fixed searching for device that never ended.

The search state got mixed up, which resulted in a search forever.
I added an explanation in main.cpp and wrapped the search for a
new device into a thread, which is needed for further versions
which do a longer search for ANT devices.
Merged branch with support to disable scan of mounted devices

Merge branch 'master' of https://github.com/LuHee/GarminPlugin

Conflicts:
	src/main.cpp

Changes in main.cpp have already been fixed on main branch
Bugfix: ScanMounted was reading boolean value from ForerunnerTools
Updated HISTORY file, with info about new feature (disable scan)