Bilingual implementation

Quick overview:

Added a language parameter to post configurations.
Added a multilingual boolean and a languages array to the brog config
Defaults to monolingual English settings.
A language selection template is needed; it is show on multilingual blogs when one hits /
When one hits /?xx where xx is a language code, the regular index template is displayed but only with blog posts whose language parameter contains xx.

I did a rebase and I *think* I captured your recent change to brogger/brog.go. Let me know if I accidentally some of your code here.