series system + acquired prayer access

prerequisites are now automatically dealt with by adding a prayer
progression to the prayerSeries JSON array. each prayer can belong to
multiple series (only Sweeping Bash actually does, though)

also, prayers now contain a property containing the DOM element which is
displayed in the acquired prayers list, allowing for easier and more
flexible access to those elements, should it be required. this will be
necessary in order to enforce strict prerequisite rules

finally, selected prayers are now highlighted in green instead of being
hidden