Start building mobile discussion page

You can see the new layout by adding ?mobile=true to the end of
a discussion url. Alternatively, you can use the "next"
subdomain (i.e. next.loomio.dev) which will default to mobile
for any page where a mobile layout exists.

The new page is using bootstrap 3, so we've had to install another
bootstrap gem in addition to the current bootstrap 2 gem. Luckily
they don't conflict at all because they are namespaced separately.

All of the stylesheets, views, and assets are namespaced in "next"
directories so development can be completely separate from the
main app.

Also, the stylesheets have all been implemented using an atomic
file-structure and BEM naming-conventions.