Merge branches 'form' and 'master' of https://github.com/makemek/cms
Merge branch 'form'
Implement is_exists to check and put identifier as param in CRUD (read)
Fix search queries
Move is_exists() method from FormProcessor to Record
Implement is_exits() in tenant class
Implement get_identifier()
Define session's slot
Check for existing content
get_identifier() should return identifying column not field's value
Implement checking for existing data in Privilege
Use validate() to check for existing data