Set user language preference through param[:locale].

This is a bit quick and dirty and is crying out for a refactor but I'm confident it will work and I really want it to be live asap. The idea is that we can announce new languages and say 'click here to use Loomio in Romanian'. also I want to make a footer that has the list of languages across the bottom of every page.
language change

This change makes it a lot easier for translators to convert
the edited-when-by-who string into their own language.

Incidentally we need to fix our time formatting asap I reckon,
those 'ago's don't translate very well.
Merge pull request #872 from loomio/hotfix/language

language change
Merge pull request #870 from loomio/set-language-pref-through-param

Set user language preference through param[:locale].
Merge branch 'master' into add-footer-w-language-select