First dispose implementations.
Dispose method in other classes.
Deleting unnecessary dispose methods.
Merge branch 'master' into dispose

Conflicts:
	test/collections/filtered_collection_view_test.dart
	test/collections/mapped_collection_view_test.dart
	test/data_collection_test.dart
Merge branch 'master' into dispose

Conflicts:
	lib/src/data.dart
	test/collections/filtered_collection_view_test.dart
tests updated
minor changes to dispose
Merge branch 'master' into dispose
Fix one test.
Merge branch 'master' into dispose

Conflicts:
	test/data_collection_test.dart
Merge pull request #13 from cleandart/dispose

Dispose