BinEditor: Fix selection behavior and painting

* there factually always is a selection (cursor position is always
selected)
* since there always is a selection, always paint a selection
* since there factually always is a cursor position where you can type
(even if you have a selection), always paint a (block) cursor
* fix selection painting in hex region to match the column painting

Reverts c4a3dbe3 and fixes the selection
on find like originally proposed by Orgad

Change-Id: Ife5395a42d35ac50103a63c77cb54491afd7dd1e
Reviewed-by: Orgad Shaneh <orgads@gmail.com>