Timeout for process instances

Add a feature that allows to define a timeout at the process definition level, which defines when a process instance should be aborted automatically.

Additional aspects:

• Provide the ability to set/change this value at runtime level as well, to override it with a potentially different value for individual process instances.
• When the timeout is reached, the process instance should be aborted.
• In addition, provide support to define a script that is getting executed when the timeout is reached.