Translations and bug fixes

I added a translation system to allow you to translate all messages in PluginManager to the language of your choice.
Also some bugs where fixed with the '/pm donwload spigot' command causing it not to work for some plugins.

If you find some translation errors let me know of them so I can fix them.
Best to report them on github (https://github.com/Lenni0451/SpigotPluginManager/issues)