Fixes #5160, BZ1082163 - limit content view descriptions to 255 chars.

http://projects.theforeman.org/issues/5160
https://bugzilla.redhat.com/show_bug.cgi?id=1082163

Note that you may need to `katello:reset` if you have content views with a description of greater than 255 chars or remove the offending row(s).