IntermediateCatchEvent/TimerEventDefinition support

[SirWaddles]

I've built support for the intermediateCatchEvent with a timerEventDefinition (although this won't quite work fully in the bundle as the delay/timers are handled separately in my instance)

At the moment, this just adds the specification, interfaces and such. I don't really understand the interim format between the Bpmn2Reader and the WorkflowBuilder. On my branch, the WorkflowBuilder creates a TimerEventDefinition and the Bpmn2Reader is expected to pass it back. This doesn't seem like it would match the style of the bundle, or fit with what I think is format-agnostic building.

The main problem is that, there is number of different types of EventDefinitions that could be submitted alongside the CatchEvent, so I'm not sure what the format would look like without using a very large switch/case or something.

I don't mind rebuilding my branch so that it only includes the new elements (mine has some other pretty significant changes as well that I don't think would work upstream.)