Merge pull request #29 from andrewbts/master

Add covariant override for convenience
added modstamps
modified stuff: modstamp
sync with Joel's branch. Modstamps in sets and network are commented out.
runId instead of runID
Merge pull request #30 from akurzhan/master

Incorporated Joel's changes
modstamps in network and sets; lat/long in node.
Merge pull request #31 from akurzhan/master

modstamps in network and sets; lat/long in node
PifProbeCoord.java - base class
Merge pull request #32 from akurzhan/master

PifProbeCoord.java - base class
Merge branch 'master' of https://github.com/calpath/model-elements
Allow null lat/long in nodes
Regenerate Node class to allow null lat/long
Re-exported scenarios from mm-network-import