Extract python plugin

Description

Related Issue

Motivation and Context

Python should not be a dependency of the Remmina core. The Python language support therefore needs to be extracted into a plugin on its own.

How Has This Been Tested?

Manual tests. Still ongoing. Posted Merge Request as base of discussion.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.