Remove import statement from __init__.py

[MarkHedleyJones]

Exceptions for this have been added to .flake8 as F401 and F403.

Background

The offending code was added as means of restructuring the project without requiring changes to the plugins.
As some plugins are developed by third-parties, they are were so updatable so this was added as a temporary hack.
This may need to wait until plugins can be updated, which would be partly fixed by solving #127, or at-least ensure that proper versioning would prevent breakages to the plugin/menu ecosystem.