[3534] Basic implementation of staging and rolling back configurations.
[3534] Logging information is accessed by getter.
[3534] Better doxygen documentation for CfgMgr.
[3534] Removed CfgMgr::getConfiguration.
[3534] Renamed CfgMgr::getCurrent to CfgMgr::getCurrentCfg.
[3534] Fixed invalid condition.
[3534] Reset unit test logger in the Daemon.parsingConsoleOutput test.
[3534] Implemented (in)equality operators for CfgIface.
[3534] It is now possible to compare two Configuration objects for equality
[3534] It is now possible to copy entire server configuration.
[3534] It is now possible to revert to a selected previous configuration.
[3534] Fixed generation of the default Kea configuration file.
[3534] Commit and rollback the staging configuration.
[3534] Logger configuration can be rolled back.

Previously, the logger configuration was applied (to log4cplus) as soon as
it was parsed. We decided in the jabber discussion that the logger
configuration should only be applied if the whole configuration goes
through. So, the logger configuration is now 2-stage: parsing and commit
as for other configuration parameters.
[3533] Reset logging when unit tests exit

Some unit tests in dhcpsrv altered the logging configuration but
never reset it. That configuration was then used for subsequent
tests and made them overly verbose.
[3533] Minor changes as a result of review.

Comments have been improved in one file.  The other contains a test
that alters logging, so a test fixture has been added that ressets
the logging back to the default in its destructor.
[3534] Addressed review comments.
[3534] Minor correction to the dev guide as a result of a review.
[3534] Refactored Configuration to SrvConfig.

This change affects many files using the Configuration object and types
derived from it.
[master] Merge branch 'trac3534'

Conflicts:
	src/lib/dhcpsrv/tests/daemon_unittest.cc