Use raw instead of cbreak mode in curses.

This allows binding keys that would otherwise be catched and interpreted by the terminal like \Cc, \Cy or \Cz.

To still allow suspending and interrupting mutt, suspend and interrupt functions are implemented.

suspend will simply signal our process group with SIGTSTP. It is bound to \Cz by default.

interrupt calls mutt_query_exit and is bound to \Cc.

This should keep the behavioural changes to a minimum.

Since the Yes/No query doesn't allow keybindings it temporarily switches to cbreak instead of raw mode. This will allow the terminal to interpret interrupt and stop / suspend key sequences for us. They might not match the configured key sequences. Such a hack might be needed at more places I'm not aware of.