Suppress keyboard input on long lasting requests

The loading screen pops up on long lasting requests that blocks mouse/touch inputs until the request /response has finished.
During that time the focus stays within the last selected control and still can be manipulated by "tab" or "shift + tab".
This behavior can result in client-side inconsistencies.

Solution:

Switch the focus to a focus-trap within the loading screen. A potential leave event on the control should not fire. After the reqeust has finished switch the focus back to the last focussed control, again without firing a potential enter event.