[DataQueryOption] Rename an enum type "SortOrder" to "SortDirection"

Because I want to use "SortOrder" for a new class which will
realize advanced sorting.
Currently REST API isn't changed yet, I'll also change it later.
[DataQueryOption] Add DataQueryOption::SortOrder struct and related types & functions
[testDataQueryOption] Add tests for getOrderBy()
[DataQueryOption] Remove {get,set}SortDirection

They are moved to EventsQueryOption although they will also be
removed soon.
[DataQueryOption] Add missing comparison of SortOrderList in operator ==
[DBClientHatohol] Use DataQueryOption::getOrderBy() instead of building the statement by DBClientHatohol
[DBClientHatoho] Remove needless incrementation of ORDER BY statement
Merge branch 'improve-sorting'