Interim networking code commit in case of dev catastrophe!

DB shape change from v29 to add peer info.
New NetworkRepository to handle above.

Peer handshaking with v2 anti-DoS PoW code.
Handshaking refactored into a state-machine-like enum.
Some peer-related API calls added.

Peers exchange pings, heights, peers.

No actual peer sync yet.

Other changes:

Peer version info taken from Maven build properties/resource file.
AnnotationPostProcessor more resilient when fetching PathItems.
Per-repository session debugging flag that can be toggled at will.
HSQLDBRepository.delete() now returns int so callers can detect
 whether anything was actually deleted.
Some renaming to settings.

src/main/resources/build.properties

@@ -0,0 +1,2 @@
+build.timestamp=${build.timestamp}
+build.version=${project.version}