Block dockwidgets

[paskino]

Uses flag NoDockWidgetFeatures which prevents a lot of complications in handling QDockWidgets and makes the GUI more static.

• Set movable to False in tabified DockWidgets both in the main window and in the result window.
• Remove default popupMenu by overloading createPopupMenu, i.e. removes the weird list of the tabs which were in a pseudo-random order. This is done both in the app main window and the right hand side main window.
• During the registration, the "Image Registration" tab appears. This is no longer floatable, movable and closable.

The 2D viewer widget appears to be a QMainWindow and not a QDockWidget, hence I don't exactly know how to set the title. I tried with setWindowTitle but it doesn't show up. https://github.com/TomographicImaging/iDVC/blob/1eae74768ef7f625fbff9042055172dfe188a4b0/src/idvc/ui/windows.py#L33

Closes #174 Closes #178

Tested on Windows.

[DanicaSTFC]

if we right click on the tabs '2D Viewer', 'Help', 'Image information', the list of tabs appears

@paskino We need to remove default popupMenu by overloading createPopupMenu in the viewer.