feat(v1.1): Default TTL and grace values

When posting messages, the "ttl" field may be omitted, in which
case the server defaults to the default TTL value configured by
the operator.

Likewise, when creating a claim, the "ttl" and "grace" fields
may be omitted to use the defaults configured for each field.

Change-Id: I38c6307377293b26370de28ffa13db22228c208c
Partially-Implements: blueprint api-v1.1-request-document-changes
Updated from global requirements

Change-Id: I077f7da22e2e70e2c08fba9e09a395350fa9cdb5
Merge "feat(v1.1): Default TTL and grace values"