Key value store for extensions to store data

[kindly]

We need to allow plugins to store information.

Each plug-in should have its own name space and allow any data to be set.

There are two options.

• make a key value table in ckan that will hold random information.
• use redis (or other key value store)

If in sql suggest schema of form:

• (namespace, obj_id, key, value [, value_type])
• value is json