Kea engineering drop is being constructed. Version number was bumped
accordingly.

Adds DHCP-DDNS to the BIND10 Guide.

Resolved Conflicts:
	src/bin/dhcp6/dhcp6_srv.cc

Added use of boolean structs for fdqn unit tests for clarity.
Minor cosmetics.

Merges in reversion of 3339 and 3373.

Added discussion of reverse DNS udpates to tables 17.4 and 18.4.
Fixed other minor typos.

Added the constant D2ClientConfig::DFT_ALWAYS_INCLUDE_FQDN

Added a method to ValueType<> template, getOptionalParam.
Defined constants for dhcp-ddns default values in D2ClientConfig.
D2ClientConfigParser uses these in conjuction with calls to
ValueType<>getOptionalParam() to ensure all the parameters needed
have values.
Modifed unit tests accordingly.

Files reverted:

Failing to initialize all values causes valgrind errors.

Conflicts:
	src/bin/dhcp6/dhcp6_messages.mes
	src/bin/dhcp6/dhcp6_srv.cc
	src/bin/dhcp6/dhcp6_srv.h
	src/bin/dhcp6/tests/dhcp6_test_utils.cc

b10-dhcp-ddns now checks for NXRRSET on DNS removal, rather than NXDOMAIN

Also moved entry 767 above the beta release line.

Python data.merge function now does "deep" merges

The merge logic was simplified a bit and the commentary was improved.

 - GenericLeaseMgrTest class moved to a separate file
 - @todo added for disabled tests in memfile (with explanations)
 - Added several comments