Make ESC exit add/remove hotkey mode.

Add/remove hotkey modes are only partially modal. If you enter one of those
modes and press ESC, it would exit the help screen (or prompt you to save &
exit). With this change, ESC will leave the modal state instead. (Pressing ESC
again will have the same behavior of exiting the help display).
fix scrolling in message window
Merge branch 'esc_from_hotkey_mode' of https://github.com/lucianposton/Cataclysm-DDA into merge
Merge branch 'master' of https://github.com/CleverRaven/Cataclysm-DDA