Removed Runcible references from filter_rule models

Redoing a previously acked pull request (PR 2084)
 https://github.com/Katello/katello/pull/2084 to update it after the new git repo structure..
Also look at https://github.com/Katello/katello/pull/1882/files#r3727099
for more info.

```
 As discussed going to hard code these content types in package.rb, package_group.rb and errata.rb and add glue layer tests to ensure that the constants are consistent with runcible. (Coming up in a diff pull request)
```