Adjust Email window to allow resizing between message and inbox

[jordan_yen]

Right now, most split windows can be stretched to give extra size to the top and bottom areas, but not email for some reason. Given the email delivery system for character items and such, it would be really helpful if I could shrink the email content area and see more of the emails themsleves (the subject area).

[FarmTank]

Because the UI is hardcoded in C from scratch this could either be really easy or impossible.  I can't make any promises until I get a chance to look into it.  However if it looks easy enough I can make a note to throw this in.

[Cinnder]

This might help solve a problem I reported on Discord a little while back where the last item in the Inbox can't quite be seen or scrolled to when the UI scale is set to certain values other than 100%.  (Mine being 116%.)