Suggest to simplify {Application,Platform} Component {Requirements,Capability}

Instead of talking about

1. Application Component Requirement
2. Application Component Capability
3. Platform Component Requirement
4. Platform Component Capability

I suggest we simplify these terms to just Capability and Requirement. Rationale is that, since these structures are all likely to be very unique, we should actually be talking about (and introducing types for) "Application Component X Requirement" etc., which would be overkill. Hence, my suggestion to use only one simple type for each.

However, as Mark pointed out, there are differences between these types on the Application and Platform side regarding whether or not they are required, etc. My sense is that we'd stand to gain more from simplification, though.

This issues was raised by Tobias and was drupal issue # 1032