Introducing a mixin for the submit buttons.
Member edit form now also has buttons at the end.
Adding some space at the page bottom.
Merge pull request #623 from NicoleRauch/master

ui tweaks
configuring add ons now inside the activity edit form
Merge commit '300a61694d85467e2ab838bdcadcf8bb25216214' into nicoleactivity

Conflicts:
	lib/activities/views/edit.jade

renamed addOn.jade to addon1.jade (interim)
rename complete from addOn to add-on
introduced AddonConfig prototype and renamed fields
showing add-on button only to registered members
introducing tabs on activity edit page