Request #30411: Free edition splash screen.

New splash screen on UNIX, including a free edition one, and a
new free edition splash screen on Windows.
The splash screen should always show up before any other 
windows.
If the free edition splash screen is not found then MLWorks does
not continue.  This is the same on all platforms.  If the other
editions do not find a splash screen then they continue normally
after giving a warning.
The free edition splash screen times out after 10 seconds without
allowing any interruption while (only on Win32 platforms) the 
other editions splash screens last for 5 seconds but when clicked
on they disappear.  This doesn't currently happen on UNIX for the
other editions but the normal splash screen only lasts for 3 
seconds on UNIX.
