Move MeshMS implementation into servald

[quixotique]

The MeshMS logic should all be implemented as part of servald, so that it becomes a “core Serval service.” A command-line and monitor API must be designed to support all the MeshMS functions needed by Batphone. The objectives of this work are:

• definition and development of the new MeshMS API should be driven by a new, complete test suite called meshms;
• the new API should permit the elimination of the Batphone message database, so that Rhizome functions as the persistent message store;
• the current Java implementation in https://github.com/servalproject/batphone/blob/development/src/org/servalproject/rhizome/Rhizome.java should be used as the reference for the MeshMS message log format, and interoperability between the original Java and new servald implementations should be proven, ie, messages sent by one can be received by the other;
• the new implementation should make use of Rhizome journaling functions to prevent message log payloads from growing indefinitely.

As part of this work, the Rhizome manifest management code in servald will need to be refactored into a more formal, efficient and object-oriented form.

[quixotique]

This work was completed by the merge commit 8a1c0a3. The new service manifest field value "MeshMS2" replaces the prior "MeshMS1".

Three automated test cases were developed.

The Rhizome manifest code was not refactored as much as hoped.