Implement custom title validation, single case.
Current progress on title uniqueness validator.
Merge branch 'develop' into feature/uniq-title2
Merge branch 'develop' into feature/uniq-title2
p/69962294 b/13886201 Duplicate title shows error in form

Also in this commit:
* 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
fixing downgrade for migration to specify that all constraints being dropped are UNIQUE (MySQL requires it)
Make zero-item lists immediately send 'loaded' event.
Merge pull request #1300 from reciprocity/feature/tree-0item-load-signal

Make zero-item lists immediately send 'loaded' event.
Merge pull request #1299 from reciprocity/feature/uniq-title2

Show error in form when a title is duplicated.
Merge remote-tracking branch 'origin/develop' into feature/harsher-input-bleaching
Fix migration ordering (due to concurrent pull requests)