Bulk modify - use new API

[dantownsend]

We added the ability to bulk modify rows:

https://github.com/piccolo-orm/piccolo_admin/issues/158

Once we've merged these changes into Piccolo API, we should use the new API for bulk updates:

https://github.com/piccolo-orm/piccolo_api/pull/145

[sinisaos]

@dantownsend I can do that if you want because I already have the code for it.

[dantownsend]

That would be great thanks!