Fix import & use of SchemaUtility to StreamSchema

Issue https://github.com/pyrocms/pyrocms/issues/3190
2.3/Dev Fix mkdir() installation error
Fix 'hidden' field error
Fix StreamSchema on pages
Fix is_unique & is_locked on install
Fix StreamSchema on users
Fix StreamSchema on variables
Merge pull request #3192 from jasonagnew/2.3/develop

2.3/Dev Fix for Install Errors (SchemaUtility, mkdir()  & hidden field)