fix(users): Fixed checking unique user fields against same user.
fix(users): added test for exclude parameter in sdUserUnique directive.
fix(users): fixed tests for sdUserUnique directive.

close #175
feat(core) : Add ability to switch client version

Introduce "beta version" switch on client.
feat(core): Add example beta module

Planning module as beta module
feat(core): Move code to separate service

Create separate service superdesk/beta and move related code there
Change the way sd-beta directive work