fix refs to css & js files
content edits requested by MN/MH
fix drop-downs

The drop-downs in main/index.html were not overlapping the content
below, but rather pushing it down.

The fix I came up with is the quickest/simplest I could come up with
that was halfway acceptable.  It's not particularly good; the problem
should be revisited at some point.

One problem I ran into is that many CSS directives I introduced were
being overruled by directives specified for the `#content` element.
Having CSS directive specified by ID for such an encompassing element
makes it difficult to specify the appearance of classes of contained
elements.  At any rate, to eliminate the guesswork, I just tacked
`!important` to everything I added to main.css, whether it was needed
or not, to protect them from being overridden by `#content`-specific
directives elsewhere.
tighten the spacing of drop-down lists

This is a minor cosmetic change: it causes the html for the drop-down
lists to be printed at one-line per element, and no whitespace between
successive elements; this was just to make it easier for me to
work/experiment with this html, especially when using my laptop.
remove stray duplicate paragraph
content edits requested by MN
fix insignificant bug
enable generation of erk table page
implement hover behavior
include linked thumbnails of matrices
fix earlier update of lookup_table.py
add MN's blurb for matrix figures
tweak offset_y
implement more prominent browse button
spruce up thumbnails box
minor edits/fixes
thumbnail imgs
change title
legend for lookup tables
various edits to lookup table page