ability to add a custom option (e.g. ticker box)

[richardeakin]

This would give users a place to check something that would alllow different sections of the cinderblock.xml to be added or excluded, similar to how you can currently add things to just a certain configuration.

Examples:

• OpenCV: users want to add in the extra gui, which we don't by default.
• PortAudio: whether or not to add ASIO as a backend on windows