Added ChangeSet toJson functionality.

It is now possible to export whole ChangeSet into JSON by using its
toJson method.
Added fromJson functionality to ChangeSet

Method fromJson creates a new ChangeSet according to the JSON-formatted
ChangeSet.
Added function apply(ChangeSet, DataMap)

Function apply(ChangeSet, DataMap) applies the changes present in
ChangeSet on the DataMap.
Updated test for apply functionality
fixed ChangeSet apply and added tests
fixed merge conflicts
Merge pull request #33 from cleandart/change_set_apply

Change set apply
Ad .DS_Store to gitignore.
Add onChange grouping support.

This enables us to listen to multiple onChange events easily.
Update version number accordingly.
Newlines.
Add reactiveRef
Increase version number.
Do not trigger change when value in data ref is same.
Merge pull request #38 from cleandart/onChange

Add onChange grouping support.
bugfix: removed, added, strictlyChanged items of changeset are now complete decomposition
Merge branch 'master' of github.com:cleandart/clean_data

Conflicts:
	pubspec.yaml
	test/change_set_test.dart
Lots of new Tests + refactor json manipulation on changeset.
applyJson works also on not cleanData
Refactor