fixes #2250 API v2 add/remove puppetclasses from hosts and hostgroups

GET puppetclasses for host, hostgroup, or environment 

/api/hosts/:id/puppetclasses
/api/hostgroups/:id/puppetclasses
/api/environments/:id/puppetclasses

ADD puppetclass to host or hostgroup (not environment)

PUT /api/hosts/:id/puppetclasses/:id
PUT /api/hostgroups/:id/puppetclasses/:id

REMOVE puppetclass from host or hostgroup (not environment)

DELETE /api/hosts/:id/puppetclasses/:id
DELETE /api/hostgroups/:id/puppetclasses/:id