Disable OSX app nap

This will hopefully help deal with a particular issue where the program
may go to sleep if it hasn't received input from the user for long
periods, or if a game is running in fullscreen mode apparently.
Fix 'possible loss of data' warning

Qt doesn't like to use size_t anywhere.
Do not draw text from file if file not found
Use better default fonts

On windows, Arial is probably one of the most commonly used.  Mac,
Helvetica.  The rest, Sans Serif.
Don't use informative text for message box

The informative text is meant to be additional information, not the main
information.  If you use informative text without using regular text, it
causes the message box to get all squishy.