Output SVG in scores
This change makes scores be outputted in SVG, and rendered in-
browser if supported. A .png fallback is also created through
the MediaHandler, for both files to be output in an <img tag
with scrset as the SVG, as discussed in T134455.
The SVG output uses the '-dcrop' option, of which is under code
review: https://codereview.appspot.com/326960043/ . This option
automatically places all the music on 1 file, of which is trimmed.
As the '-dcrop' option outputs a trimmed file, the $wgScoreTrim
global has been removed as it is now automatic. Further, the
multipage functionality has been removed since all is outputted
in 1 file.
DO NOT MERGE UNTIL -DCROP IS RELEASED UPSTREAM.