Verovio rendering of incipits not working for previews

[Peter Stadler]

Originally reported by @KristinaRichts

[Peter Stadler]

@MauPalantir already did some related work in #36 and it seems we simply need to switch to https in

MerMEId/style/mei_to_html.xsl

Line 121 in 862df6d

 <script src="http://www.verovio.org/javascript/develop/verovio-toolkit.js" type="text/javascript"> 

as well.

But since the asm.js version is obsolete (see Verovio docs) this looks like a temporary workaround. Will do so nonetheless for now …