Revert "PloneLanguageTool tests have been moved to p.a.testing."

This commit breaks the AT tests.

This reverts commit 6c43051c980964d8fb2a2c38366c44bec77b12e9.
Revert "Checkout P.PloneLanguageTool."

This commit breaks the AT tests.

This reverts commit 2495e6abf9f4b980aabfda49f7dacfd113c530e0.