Merge pull request AltBeacon#494 from AltBeacon/fix-singleton-creatio…

…n-thread-safety

Ensure singleton object creation thread safety

Attempt to syncronize beacon parsers

Check of bluetooth LE is available before starting/stopping scanning …

…to prevent a crash due to stack overflow

Prevent crash due to null beaconManager by getting instance before st…

…arting power save callbacks

Merge branch 'master' into access-persisted-monitors

Merge branch 'master' into access-persisted-monitors

Don't start or stop scans if bluetooth state is off to prevent crashe…

…s on HTC devis

Don't implicitly require bluetooth in manifest

Don't implicitly require bluetooth in manifest

Merge pull request AltBeacon#419 from AltBeacon/limit-scans-on-android-n

Avoid spurious entry/exit events on Android N