Clean up localization - fixes #760, modifies pull request #755
- make all file loading relative to module base
- move core language files into appropriate place
- eliminate all SetLanguage commands and use SetPreference instead
- eliminate all LoadLanguage commands except for core's
- fix duplicate keys in JSON language files
- remove BOM from JSON language files

OPEN - task 760: Translations not being loaded from built kit 
http://github.com/OpenRefine/OpenRefine/issues/issue/760