Refactor subscription logic

[marcelveldt]

Refactor of the subscription logic for both optimizations reasons and less traffic (prevent congestion).

• Run interviews and subscriptions in parallel tasks to speedup startup.
• Only subscribe to specific attributes
• Detect endpoint additions and removals on bridges

BREAKING CHANGES

• Schema is bumped to version 4
• All nodes will be re-interviewed
• Attribute changed callbacks will not happen if attributes are not specifically subscribed
• Within the client implementation, the 'get_nodes' and 'get_node' methods are changed from coroutines to regular methods.