Fix #13

As this is a fairly major change in the protocol, and because it changes
the syntax of the PING command I've renamed PING to HELLO (which is a
bit more descriptive of its function given that it is now required to
precede any commands from a client).

Also refactored exceptions, warnings, and network repeater codes into
their own modules.
Fix #3

Add Qt4 as a client dep. At this point the GUI should be fully
functional (more or less!)
A little tidying up

Moved picamera import to where it should be (now that 1.4 is out) and
added a warnings handler to tidy up the output
Remove some console spam

When using the GUI
Fix #12

Loads of additional protocol bits to support all the camera's dials and
knobs...
Add documentation for #12