Headless Qunit reference fix
Add test for group adding and removing
Rework Children

Instead of an id-indexed object, the children property is now an array.
This makes it many times faster to iterate this property and leads to actual
performance gains (see also http://jsperf.com/performance-of-array-vs-object/3)

It's not a plain array, but an array with superpowers: You can still access the contained
objects by id by doing children.ids['idOfTheObjectIDesire'].
This works, since this Array intercepts all push, splice etc. calls
and updates the ids property on every modification.

This commit also simplifies the group adding/removing methods.
Most of their work is now being handled by the generic object.replaceParent() method.
Add more tests, modify a few who accessed children by id instead of index.
Can safely add garbage to group
Make parent.additions/parent.substractions an array of objects, instead of an array of idstrings.
Fix for removing objects that have just been added
Move JSHint config to .jshintrc file
Fix a few undefined vars
Move replaceParent funtion
Fix merge
Object.children.id -> Object.children.ids
Merge pull request #110 from DieBuche/ChildrenAsArray

Rework Children property to be an array