added generics to DataMap
removed .DS_Store
removed unnecessary .DS_Store
added types to DataReference
Added generics to DataList
Added generics to DataSet
Merge branch 'master' into generics

Conflicts:
	.gitignore
	lib/src/data_reference.dart
	test/data_set_test.dart
Merge pull request #37 from cleandart/generics

Generics added to DataMap