Added languages compatibility, added french translation

Changed css to get the plus icon from plugin dir instead of direct
access (may prevent a bug with directory name change or case sensitive,
etc.)

Note: I used the version from wordpress website instead of this because
there was annoying user agent stuff, don't know what they were used for.
Fixed a search and replace issue with _e

(typed e_ once and search replaced like hell)
Everyting works fine now :)
Merge pull request #2 from GabLeRoux/master

Added translations! :D (and fixed my mistake!)