Alle phpBB Dateien sind GPL v2 nicht nur die für phpBB3

Fix #52
Rename license.txt to LICENSE

That's also what the validator wants to have

Fix #52
Merge pull request #53 from nickvergessen/issue/52

Issue/52

* nickvergessen/issue/52:
  Rename license.txt to LICENSE
  Alle phpBB Dateien sind GPL v2 nicht nur die für phpBB3
Add language pack validator to composer.json and run it on travis
Move LICENSE files in place
Merge pull request #62 from nickvergessen/issue/61

Add language pack validator to composer.json and run it on travis

* nickvergessen/issue/61:
  Move LICENSE files in place
  Add language pack validator to composer.json and run it on travis