Added French translation

Translation mainly rely on YouTube's translation.
Merge pull request #2 from GeoffreyFrogeye/master

Merge from original
Updated french translation for v0.5.1

Placed directly in _locales.
I made some alterations from the original, e.g. "vidéo" (video) is replaced by "lecteur" (player) because it sounds way less weird.
I've also not seen "toggle_disabled" and "size_checked" & "size_unchecked" description in the extension, so verbs conjugation may seems out of context.
Deleted /_locales/partial/fr.json

As /_locales/fr/messages.json is no longer partial, this file can be deleted.
Updated french translation mistake

Finally found the context of "toggle_disabled" so I corrected the translation. Good thing that I had to listen to a music that I didn't have in my library.
Merge pull request #36 from GeoffreyFrogeye/frenchTranslation

Updated french translation for v0.5.1
Spanish translation

by David Suarez
v0.5.2
remove unused 'description' properties
toolbar speed unchecked if it's set to x1
default download attribute
v0.5.3
Merge pull request #4 from chrisrobins/master

Update from v0.5.3