Final (alpha) fix of getter-setter patterns

Getter-setter have all been checked to adhere to standards set by IRC committee, specifically they should use boost::optional and boost::none_t as agreed. Please check the supplied image for correctness.

Only changes in this pull request affect "removeReference" & "hasReference" in "SimpleTag" & "DataTag": for both now only "const string &id" versions exist. The "TestSimpleTag" test has also been fixed to only use those versions.