Add zoom % indicator about music-scholars-annotator

[alastair]

This is interesting, because as far as I understand "zoom" in verovio is a bit different to normal document viewers anyway, right? If you zoom in, verovio will re-render a smaller number of bars of music, at a slightly larger size. Does this make sense to indicate in terms of percentage? I don't think it maps to the idea of zooming a PDF very well.
We could just have a numerical "zoom level" indicator which shows how many times the user has clicked the zoom in button

[fedezubo]

yeah, in theory you could zoom down to 1 single note and have it occupy the whole screen. I think that zoom levels should be the way to go... like the standard is 3 going up to 5 and down to 1 or something like that

[fedezubo]

fixed locally