Full Spanish translation from tu_79 integrated + localisation fixes

I went through this twice line by line to catch any possible mistakes.
In the process, I caught several older localisation mistakes as well.
They are, of course, lost in the line noise (har har) of this massive
text update.
Added column headers (language keys) to all localisation files
Merge pull request #148 from zijistark/alpha

Full Spanish translation added + localisation fixes