The old approach of including the same source files into
multiple places is less than pretty.  But moving the code
to libply didn't seem right either, since libply is fairly
generic and could in theory get swapped out with a standard
runtime at some point.

Also, exposing libplybootsplash as an external library will
facilitate creating out of tree splash plugins.

Previously, they were still using blue.

Previously we've just hard coded the location to the fedora
logo.  Now it's a configure time flag.  We also have a configure
time flag for a background color that goes with the logo, but
none of the splash plugins make use of it yet.

This is a first step toward making the window provide
an draw handler interface, so we can hide the details
of pause/unpause, resetting raw mode, and graphics mode,
etc from the individual plugins.