Is_ in installer

Should take care of: https://github.com/pyrocms/pyrocms/issues/3244
Doesn't need to be unique - the constraint lives on the table for slug / lang
Install method for streams based tempaltes
Merge branch 'refs/heads/2.3/develop' into 3.0/develop

Conflicts:
	system/cms/modules/templates/details.php
Merge branch 'refs/heads/3.0/develop' into AIWS/production