Fxies #5181/BZ1110955 - add API for available composite content views.

The bugs mention that the total is incorrect when using the select all
control.  This was due to Bastion transforming the response from the index
call on Content Views and hiding non-applicable results.  This commit
moves that logic to the server side where it belongs.

http://projects.theforeman.org/issues/5181
https://bugzilla.redhat.com/show_bug.cgi?id=1110955

FYI, I created an issue for this.

http://projects.theforeman.org/issues/6438