258 Fix gem and plugin issues

Fix #258 - remove gem jazz hands and replace with gem pry-byebug depending on `ruby -v`
Fix #279 - remove plugin dynamic_form and replace with gem dynamic_form
Fix #130 - remove plugin multiple_select and replace with gem simple_form

For the future:
Fix #134 - remove plugin simple_time_select (wait for branch merges)
Fix #280 - remove plugin rails_upgrade (still need to upgrade fully before removing)
IMO we shouldn't support a JavaScript-less environment. JS has been a standard web technology for a long time, and retaining legacy code will just cause more bugs in the long run.