Update tests to use plugin folder structure

[obenland]

Makes it easier to identify file relationships between test and production files and makes filenames easier to read.
It does add a bit of overhead with the namespace being applied to all test files now.

Proposed changes:

• Mimics folder structure in tests as they are in the plugin.
• Adds missing namespace declarations to test files that don't have them yet.
• Updates filenames to be in line with their production counterparts.
• Fixed a test that failed after the load order changed.

Other information:

• Have you written new tests for your changes, if applicable?

Testing instructions:

Unit tests should suffice.

Before	After

[pfefferle]

this is (despite of the name) in the root includes folder. Just to keep it consistent, until it will be deleted by the inbox PR ;)