GitLab

 - upgrade 2.0 to 3.0 script added
 - added unit-tests
 - dhcpdb_create.mysql script now uses the same database

# Conflicts:
#	doc/guide/logging.xml

 - Added rationale for ptimeToText, durationToText
 - Added missing headers
 - Removed the default values in addValue()
 - StatsDuration is now passed by reference

1) Removed the srv-hooks logger
2) Updated DHCP4_NCR_CREATE message description
3) Updated logging doc.

Also, renamed loggers.

Except user guide related and "fixme" leftovers.

 - {ptime,duration}ToText moved to lib/util
 - missing comments added
 - EXPECT_EQ -> ASSERT_EQ
 - several consts added
 - protected methods are now private in Observation
 - tabs converted to spaces

because that directory name doesn't exist with the installed version
of kea.

This is trivial and I commit to master without review.

The erase function was called on the const_iterator which caused build
failures on Linux boxes with gcc. This fix was okayed on jabber.