[#35,!517] Added function to move of DDNS cfg elements to global scope to SrvConfig

[#35,!517]  Added function to move of DDNS cfg elements to global scope to SrvConfig

src/lib/dhcpsrv/dhcpsrv_messages.*
    DHCPSRV_CFGMGR_DDNS_PARAMETER_IGNORED
    DHCPSRV_CFGMGR_DDNS_PARAMETER_MOVED

src/lib/dhcpsrv/srv_config.*
    SrvConfig::moveDdnsParams() - new method to move
    parameters from dhcp-ddns to configured globals.

src/lib/dhcpsrv/tests/srv_config_unittest.cc
    TEST_F(SrvConfigTest, moveDdnsParamsTest) - new test