Fix line-endings.
Never redirect to the home page.

This behaviour was put in to redirect to the concerts' admin page if there
were no concerts. This no longer works because the admin pages are in a
separate area, and so it was redirecting to the homepage instead. Sort it
out.
Introduce a ConcertsIndexViewModel.

Also tweak the View to use this and not bork so easily when some bits of
the ViewModel are null.
Tidy up the display of the side bar.

Upgrade the classes to Bootstrap 3.
Display the Archive page as fallback.

If there are no upcoming concerts, display the concerts' archive as this
is the next most useful thing.
Merge branch 'bugfix/concerts-homepage' into develop