Bulk modify - use new API

[dantownsend]

We added the ability to bulk modify rows:

#158

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

piccolo-orm/piccolo_api#145

[sinisaos]

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

[dantownsend]

That would be great thanks!