Directional keyboard navigation

[akhilman]

At the moment it is possible to switch the focus between the widgets using the tab key, but it is slow and not a convenient way.

I suggest to implement switching in directions: up, right, down, left. Or even switching using the direction in degrees and acceleration to use all the features of the gamepad's analog stick.

We can also make two modes as in VIM: the selection mode, when the user selects the widget, and insertion mode, when events is transmitted to the widget.

This control should have a separate API, and not be attached to the specific keys. Thus, the user will be able to bind these commands to the keyboard arrow, to the HJKL keys, or to the gamepad.

This feature can use the widget location cache generated for #724.