Selectively hide boxes and arrows

[robander]

Major updates to JS code accumulated over the last year of development, finally bringing up to date with this copy:

• Several minor fixes, largely around spacing
• Updates to use Plex and Unicode fonts by default, with existing Arial / Helvetica still present as fallback
• Add unique class to each boxed component, which disables display of the box border for most components (keeping them for fragref)
• Add unique class to arrows based on their purpose; hide most arrows, apart from start/end and repeating groups