update the 'create silence' page config vars
update the 'create silence' page config vars

This commit updates the config values introduced in sensu/uchiwa#584
to match their move into a subhash

Addresses sensu/uchiwa#531 and sensu/uchiwa#538
Requires sensu/uchiwa#584

Change-Id: I57bed839c5dc7dc1a1895d9c98e896db224448ef

sensu/uchiwa-web,palourde/uchiwa-web,sensu/uchiwa-web,palourde/uchiwa-web