Adding first pass stuff for replication.
Tested replication and it passes first attempts.
Adding Machine tag to datacentre.launch
Fixed empty list error.
Added dump and restore.
Working and tested dump and restore with time bounds.
Added some minor sanity checks.
Finishing off replicator node.

 * Added to launch file
 * Added to README
 * made client time 24 hours
Switched default time to 24 hours ago rather than now, to allow easier use in scheduler.
Change action definition to use duration into the past.
Changed collections type to StringList to allow for datacentre comms to task schduler.
Merge pull request #50 from Jailander/hydro-devel

Adding Machine tag to datacentre.launch
Merge pull request #49 from hawesie/hydro-devel

Added replication for message store
Waiting for datacentre.
Merge pull request #51 from hawesie/hydro-devel

Waiting for datacentre.
Merge branch 'hydro-devel' of https://github.com/strands-project/ros_datacentre into hydro-devel