add registration form.
Add new scoretype NamedGroup

NamedGroup is a integration/improvement of Group{Min,Mul,Threshold}
scoretypes. Main improvement is that in NamedGroup, one testcase can
belong to multiple subtasks. This leads to consistency of judge results
and resource saving.
Adopt YamlLoader to NamedGroup.
Merge branch 'namedgroup-20140131' of https://github.com/qnighy/cms

Adding NamedGroup score type
Merge branch 'registration-form' of https://github.com/qnighy/cms

Simple registration form for new users