Giant refactorizing for localization

It is me again, I rewrote almost every layouts in order to have localization.

I tried not to broke anything, but it is pretty hard to confirm that even if this should be fine.

I removed almost every hard coded strings which have no parameters. Application is thus almost fully translatable to other languages.

If this PR is merged, something about **stop hard-coding texts** in the guide lines would be great ;-)
pref_keys.txt should be unaltered.
this includes NOT chaning misstakes (cause it will break upgrade)