fix scanning for psr-0/psr-4 type modules for admin capabilities.

fixes #1679 Also correct some general module scan issues and make sure translation domain is loaded with correct key.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #1679
| Refs tickets  | -
| License       | MIT
| Doc PR        | -