Fixed enable/disable rules for movement providers

[Malcolmnixon]

This fixes issue #139 where movement providers were inappropriately invoked. Now the movement provider is invoked if either of the following is true:

• The movement provider is 'active'. An active movement provider is always invoked, even if it's to let the provider deactivate and send finished events.
• The movement provider is 'enabled' and no higher priority movement provider has pre-empted control with an exclusive movement.