Fixed: page-based navigation now works again

-Changed initialPageHeight/Width settings to pageHeight/Width

-Added vida-direction-control class for next/prev page buttons

-Framework for grid toggles included but non-functional

-Took off page arrows when in horizontal mode

-Added "vida-svg-wrapper" class to scroll with SVG objects

-Fixed page navigation
Fixed: only one vida-svg-wrapper exists now

Also moved scrollToPage functionality into a separate function with a scrollToCurrentPage shortcut.

Refs #8
New: scrolling updates current page number

-Added border to settings for clarity and relaphabetized

-Added pageTopOffsets array to keep track of this information; array gets populated on reload

-Added updateCurrentPage function to update current page number on scroll

-scrollToPage now uses pageTopOffsets and does not trigger above scroll event

Resolves #8
New: supports WebWorkers

-Switched to up-to-date verovio-toolkit (with one comment)

-Moved all interactive code to verovioWorker.js

-Condensed navigation CSS hiding/manipulation

Resolves #2
Fixed: converted inconsistent whitespace to all-spaces

As per https://github.com/DDMAL/vida.js/commit/aa08b524ef071c939a25e9e1c56c1e729dd0253a#commitcomment-8862591
New: popup to show when WebWorkers are processing in background

-Added loading popup with non-transparent background to show when WebWorker processes are occurring in the background.

-Commented out grid toggle
Fixed: page size remains constant when zooming

-Removed extra newline in CSS

-Moved pageHeight and pageWidth recalculations to reloadOptions() to make sure they are updated frequently enough.

Resolves #9