Translation loader now ignores non-directories

I was having an issue with habitrpg failing to load when OSX created a .DS_Store file in the locales directory. This code fixes that by ignoring all ~~hidden files (files that start with “.”)~~ non-directories.

Edit: new summary of the entire pull request:
* Locale loader will ignore anything that's not a directory (previously the entire program would crash on load if there was a file in ./locales)
* When loading individual translations, only json files will be used to import the strings