Collection level write permissions

[jayrbolton]

One way I was thinking:

• create a unique namespace with some collections, receive a write token for that namespace
• use the write token to update that namespace
• generate another write token using an existing write token to add another writer

Anybody with a kbase developer token can create a new namespace. The namespace write token only controls updates. User can execute stored queries on any namespace as normal.

cc @JamesJeffryes