Delete obsolete implementation of collection transformations
Refactor to use withou ChangeSet.clear().
Refactor model.
Add ModelView and ModelViewMixin classes.
Refactored collection.
Remove unused import.
Merge branch 'master' into refactored-collections

Conflicts:
	lib/src/childcollection.dart
	lib/src/filteredcollection.dart
	lib/src/sortedcollection.dart
	test/filteredcollection_test.dart
	test/sortedcollection_test.dart
Rename suborov, tried a metod. Pridany ChangeSet.clear().
Odobrana changeSet.clear
Added FilteredCollection class; renamed methods in ChangeSet
collection.where berie ako parameter filtrovaciu fciu + Refaktoring FilteredCollections/testov.
Fixed incorrect behaviour of ChangeSets in Data. Respective tests added to data_test.dart.
Fixes from review comments on filtered collection.
Merge pull request #3 from hleumas/refactored-collections

Refactored collections