Add equipment overview to mobile site
Simplify rendering of exercise overviews

This makes rendering easier and the template filter 'get_active_exercises'
reduntant. And while the 'regroup' tag does hit the database quite a
lot, it doesn't hurt since the whole HTML block is cached.
Fix some tests for mobile
Use an accordion to show group exercises by equipment

This makes better use of vertical space (there can be any number of
equipment entries while the exercise categories are more or less fixed)
and provides a better overview. Also update jQueryUI to the latest
version.
Cache rendered equipment list, add tests