Add token management to Background manager.

This is an initial stab at adding token management to the background manager.

Token manager is broken out to a separate gen_server.
Token calls are available in the background manager and proxied to the token manager server.
Changed enabled/disabled in BG manager to affect BOTH subsystems.
Renamed enable/disable for locks to enable_lock/disable_lock to match API for tokens: enable_tokens/disable_tokens

Comments are welcomed.