spanish es_es translation

I committed a Spanish es_es translation.
There is a problem with this because you do not define UTF8 on the webpages so it shows incorrectly.
This is a typical with English developers where there are no special characters, so you don't have to "fight" with that. I added the UTF8 meta directive to some pages and the translation showed up correctly, but since each script has it's own repeated header, it is a bit tedious to fix. I would like to attend that by factoring the header code and will do so next, so I can use the backend in Spanish.
I will advise when I commit the change.
In that sense I would like to participate in the project because it looks really promising, you are doing a very good job.