Readme.md: proper table HTML markup.
CONTRIBUTING.md: Fix typo.
Fix the Changelog.

Pushed last commit way too quickly to be on time for the nightly...
Fix the installer after 3545df49b654a3fa434b3a1dd7c4be324b09e85f.

Completely forgot to actually add the non-custom messages part...
Update translations from Transifex:

 - Greek.