Show error in form when a title is duplicated.

* LocalStorage and LocalListCache updated with some fixes surrounding objects replacing current data with stale data
* Exception for duplicate titles and codes/slugs is more descriptive
* mixin created for unique title enforcement, using can/map/validations
* Added support for suppressing errors in computed_errors compute -- useful for not showing validation errors immediately when spawning a new object form.
* Error suppression turns off as soon as the user starts interacting with the form
* A migration that enforces uniqueness for titles on some tables -- if duplicates already exist they have the object ID appended in parentheses

Ref p/69962294 b/13886201