Feature/244 plugin manager

Adding a plugin manager to enable/disable plugins on demand including persistence of the settings.

Currently only the touchcontroller plugin can be managed.
check out the src/plugins/plugin-manager/Readme.md for details

here are a few revering commit in the log because I had the indicators for depth hold and laster mix into this branch

this fixes #244 
Out of curiosity, why the change from /usr/local/etc to ./etc  Do they mean they same thing?