MAGN-741 Fixed Zoom level is too fast after fit view or switching workspace

Switching between workspace will run dynWorkspaceView_DataContextChanged, adding event handler to the data context.

After multiple switching between workspaces, multiple same event handlers are added to the same data context. Therefore when there is a zoom, the event handler will be called multiple times causing zoom level to be too fast.

Solution is to remove the event handler before adding for every onDataContextChanged.