Add possibility to add and a remove a local convnetion for testing

Functions `add_convention` and `remove_convention` would be nice to have to locally test new conventions.

`add_convention` would get a path to a csv of json file to be copied to the *conventions* folder and than call `sofar.update_conventions._compile_conventions`. `remove_convention` gets a convention name as str and removes it from the *conventions* folder.