Revert the opening of workflow through store id (!308)

In !308 (merged), I introduced the currentWorkflowId store to keep the id of the current workflow stored when switching between Edit and Monitor and restore to the canvas the opened workflow when landing on Edit again.

Unfortunately, I went too far in !308 (merged) and used currentWorkflowId to open all kind of graphs (when selecting from server, from the disk) by rerendering the EditPage.

Not only this went beyond the scope of the needed feature, but it brought unwanted rerenders of the EditPage producing app-breaking bugs (e.g. #187 (closed), #190 (closed)).

In this MR, I essentially revert !308 (merged) until I find another quick solution or until we review the flow of loading/restoring workflows. Conceptually, it means that setting/resetting the currentWorkflowId is reverted to setting/resetting the working graph directly via setWorkingGraph