Adding Spanish and starting the final tweaks 

Hi @joelmeyerhamme!

I spent some time adding the spanish translation so I thought I PR you so you can centralize this efforts.

I also fixed an error related to the use of ``ActionSupport`` ``presence`` method and I made the string where dates are excluded, more clever.

Please let me know what you think,

David

Ah, and great job starting this internationalization efforts! Thanks :+1: