Commit missing icon images for jQueryMobile
Make sure all sets in a superset have the same amount of repetitions

Otherwise it doesn't make sense, this fixes #54
Don't pop from empty step list, this fixes #55

If the user didn't add any repetitions to the workout, the timer isn't
very useful anyway, so just ignoring this is OK.
Add some explanation text about how to enter the repetitions
Globally disable jQueryMobile's AJAX navigation

This was making too many troubles with many different things, once a
solution is found, this should be removed.
Comment function with a docstring
Improve the workout page when exercises don't have repetitions.

This is done with a flag in the canonical representation and while
strictly speaking this is not necesary, it simplifies the template logic