Abstract: add cascade fixes issue with updates
model.js: toObject converts "" to null
editor.js: cancel editing in modal boxes
editor.js: refactoring method names
editor.js: display character limits in text editor
Abstract: add isTalk and reasonForTalk
Model: new model for topic

Move model AbstractGroup to own file
Model: better equal method
Topic: add toString method
Conference: add topic to conference model
Topic: support topics in assets, services and js models
Bootstrap: add glyphicons
editor.js: improved editor
Tests: small fix in assests
Merge pull request #90 from stoewer/master

Again an improved editor

LGTM