Add prev/next buttons and hotkeys

This adds left/right arrows to the BioDalliance popup, plus left/right/escape keyboard shortcuts.
This is going to be massively slow every time you click the next arrow… it may be time to implement a better solution (maybe a CHROM -> POS sorted trie, maybe just keeping the master copy sorted by pos and filtering through, maybe something else). This could take, I believe, around 700ms on 45k records *each* time you step to the next one. A hacky quick fix could involve indexing the DOM instead of resorting an then indexing the records themselves. Not sure I'd condone that, but…