Add support for the Open Pixel Control protocol.

This is just missing the final code for the OPC client.
Finish off the rest of the OPC code.
Fix lint and license warnings.
Add the client test, fix a bug.
Fix a memory leak and build warning.
Merge branch 'master' of github.com:OpenLightingProject/ola into opc
Add the GPIO plugin.

I need to do some timing tests.
Merge branch 'master' of github.com:OpenLightingProject/ola into gpio
Merge branch 'opc' of github.com:nomis52/ola into gpio

Conflicts:
	common/protocol/Ola.proto
Add the missing Makefile
Address the first of Peter's comments.
Minor fixes to the GPIO plugin.
Merge branch 'gpio' of https://github.com/nomis52/ola into opc
Doxygen fixes
Fix some more of Peter's comments.
Address the rest of Peter's comments
Fix another comment.
Merge pull request #562 from nomis52/opc

Add support for the Open Pixel Control Protocol, Closes #502.
Move GPIO writes to a separate thread. Fix some bugs.
Another GPIO fix.