Implement CI build/test project actions

[cefect]

A nice CI primer can be found here. Once setup, this will reduce development time and reduce bugs for the users (improving their experience).

Need to figure out how to setup a pyqgis build on GitHub. I'm guessing we won't be able to execute UI tests remotely. If this is the case, we can only include API/backend tests (which we'll need to write.. see issue 65).