ArkViewer: close on Escape

BUG: 386729
FIXED-IN: 17.11.80

Test Plan:
Open preview for a text file, then check whether Esc closes the window.
If some operation is happening in the kate part (e.g. text selected, or search bar open),
make sure Esc aborts the operation rather than closing the window.

Reviewed By: broulik

Differential Revision: D8761