Allow to select a Range of bytes by specifying the start and size

[jeffli678]

In hex view, currently we can only select a range of bytes by mouse dragging. However, it is quite often that we know the start and size of the range. It would be nice if we can make the selection by specifying the range.

[xusheng6]

Added via 015314d, should be available in dev 4.1.5260