Add command console support to QAspectEngine

It would be very useful to be able to issue commands to the QAspectEngine to make it perform various actions or to delegate the commands to a particular aspect (or set of aspects).

A function such as executeCommand(const QString &command) on QAspectEngine is likely sufficient for now. A simple command parser should be able to process or delegate commands.

Some possible examples:

• "list aspects" should dump out the names of the registered aspects.

• "render list buffers" or maybe "list render buffers" should delegate the "list buffers" command to the render aspect which should then dump out some info about any Buffer objects it knows about say the handle, the QNodeId of frontend object, frontend object's object name etc.

• "render show buffer -handle <handle>" or "render show buffer -id <nodeId>" should dump out more detailed info about a particular Buffer

• "render stats buffer" could maybe dump out information about how much memory is used by buffers, how many attributes refer to each one etc.

The important thing for now is not really the specific commands as we can extend these later without changing the api. But getting some simple semantics in place for example commands would be nice.

We can add a convenience console gui component at a later date a la quake's console.