- translations fallback to english by default (customizable in config file)
- adding a few strings that weren't translatable before
- 'translationAvailable' plugin information entry is now optional (defaults to false)
refs #251

git-svn-id: http://dev.piwik.org/svn/trunk@518 59fd770c-687e-43c8-a1e3-f5a4ff64c105