Renames package to mija to avoid confusion.

- mija (with an I-breve), I guess is the new name of the project
- this allows a clear distinction between components of this app and core module, and the concepts belonging to the Imgur api
- a workflow for authentication is started too (wip)
Removes dupe code, renames interface
Fixes build.gradle so it generates ApiConstants in correct place.
Renames to mijur (mija has unfortunate meaning in another language)
Merge branch '2_authenticate_to_api' into dev