Address conflict with Synchronet internal mouse support

1. Don't enable mouse support if the user's terminal is configured to not
   support it.

2. After calling bbs.receive_file() which displays a menu and uses sbbs's
   internal mouse support, which enables a different mouse reporting mode,
   disable the console.mouse_mode (sbbs's internal mouse support) before
   re-enabling the mouse support for the avatar_chooser's own custom mouse
   mode. Fix fixes issue #414 reported by Nelgin.

3. Fixed a typo in a message displayed to user if avatar upload failed.