CMS-2278 Make Schema Manager use new REST API for doing create and update

ContentTypeWizardPanel, RelationshipTypeWizardPanel and MixinWizardPanel are using new REST API now, ContentTypeResourse
was updated to accept JSON in create and update endpoints, also unit tests were added for content type create and update services.
Merge pull request #418 from enonic/CMS-2278

CMS-2278 Make Schema Manager use new REST API for doing create and updat...