Fix for PAL7823 (checking for if study is locked before doing New Dataflow command).

Fix for PAL7823 (checking for if study is locked before doing New Dataflow command).
Also some re-engineering of the code: new function createDataflow() is introduced, it combines functionality of the 3 commands: newDataflow(), importDataflow(), modifyDataflow().  These 3 functions did basically the same thing, with slight differences, which are implemented in createDataflow() using 'mode' parameter.