Revises Makefile to copy schema document over to the
installation directory. `glib-compile-schema` will be
executed there, as it may contain other schema files
from different plugins. Doing this locally and then
copying over the resulting `gschemas.compiled` file
will overwrite any schemas already there. This is
obviously undesirable.

Signed-off-by: Jim Teeuwen <jimteeuwen@gmail.com>