Enables script access to the per object dynamic attributes through the JsonStore
script functions. Adds JsonAttachObjectStore to associate a store identifier with
an object (scripts can only access the store in their host object, this could be
extended but isn't necessary for now).

Note this opens a method to the DAMap OSDMap. This will be removed later, but
greatly simplifies the code for now.

The JsonStore and these scripts are disabled by default.
Merge branch 'master' of ssh://opensimulator.org/var/git/opensim