`Mastr.home_directory` does not return a self defined path

[FlorianK13]

You can define a path for your open-mastr directory by using the env variable "OUTPUT_PATH". However the Mastr.home_directory attribute only returns the hard coded ~/.open-mastr. The variable self.output_dir instead returns the correct path.

home_directory is not used in the code base, so I think we can savely delete it.

[FlorianK13]

This is actually part of #689 and will be worked on there