qdoc: Handle scripts exactly like styles

qdoc: Handle scripts exactly like styles

The values of the scripts variable in the qdocconf file
must now be paths that are relative to the location of
the qdocconf file, just like for styles. They can be
absolute paths, of course, but if they are relative,
they must be relative to the qdocconf file containing
the scripts variable.

Task-number: QTBUG-27878
Change-Id: Iec12d1937ca9db540a2aa5e378fadc60de0a2d8c
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>