Make assertions a little more expressive
Change Activity API: registeredMembers is now a function, not a direct property access
Extract registeredMembers into Resource object (rather mechanically for the first step)
Fix loading of registeredMembers from Resource
Move member add/remove from Activity to Resource
Use dictionary to store Resources instead of array (allows acces by name)
fixed typo on goodbye
Make modes of Activity construction explicit
Change values of exisiting activity object instead of recreating it

Fixes bug that we lose registered memebers when editing the activity.
Merge pull request #447 from leider/master

stylesheet compiled from sass
Merge pull request #443 from fhopf/typo

fixed typo on goodbye
Note areas for improvement
Merge pull request #448 from wosc/limited-activities

Introduce Resources for Activities