Start previous message log at bottom

The log that appears when pressing Ctrl-P now displays as if the player
had pressed End themselves.

This is done with a new function named curses_display_menu_bottom().

Closes #53 on GitHub.
Adding autopickup/msgtype rules scrolls to bottom

Adding a new autopickup or msgtype rule will show the menu of rules
scrolled to the bottom, so the newly added rule will always be visible.

Closes #54 on GitHub.