Pluginizing the DNP3 analyzer, plus a basic script logging requests
and replies.

Almost ready, but now 1 test fails again ...

[Note I broke git history by copying over the files into a new branch.]
Merge branch 'master' into topic/robin/dnp3-merge-v3

Conflicts:
	scripts/base/init-default.bro
Fixing well-known port.

This fixes the remaining test.
added condition to check DNP3 packet without app layer data

Conflicts:
	src/analyzer/protocol/dnp3/DNP3.cc
added a test case for dnp3 packets with only link layer
Tiny bit of cleanup and adapting the new test.
Merge branch 'topic/robin/dnp3-merge-v3'

Includes a bit more docs/comments cleanup. We should eventually
document the events further but it should suffice for now.

* topic/robin/dnp3-merge-v3:
  Tiny bit of cleanup and adapting the new test.
  added a test case for dnp3 packets with only link layer
  added condition to check DNP3 packet without app layer data
  Fixing well-known port.
  Pluginizing the DNP3 analyzer, plus a basic script logging requests and replies.
Updating submodule(s).

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