Fix beginBroadcast called while already in a broadcast

for updatePlayerSubscriptionState.

By counting the number of registered callbacks, thus eliminating the need
to call beginBroadcast to get the count.

Also remove the requirement that scrobling turns on second to second
updates, because we already receive (and handle) these events from the
notifications enabled by the listen command.
Fix beginBroadcast called while already in a broadcast

by having the executor run all broadcasts, which ensures sequential
execution.
Update gradle plugin version
Merge remote-tracking branch 'kaaholst/bugsense' into develop

* kaaholst/bugsense:
  Update gradle plugin version
  Fix beginBroadcast called while already in a broadcast

Conflicts:
	gradle/wrapper/gradle-wrapper.properties