Lightsheet: Channel#0 shall be green (data), channel #1 red (ref), according to David
Add infrastructure for a 'loading' indicator; unused yet

Using this for frame loading is non-trivial as a frame change will
trigger re-render of the webgl-controls template; we need to fix that
first. However, this will become useful for other purposes too. :)
computation-server.py: Proof-of-concept computation services provider

Currently, we provide just bounding box intensity plotting.

This is not integrated in simple-hdf-server since these serve different
purposes; most importantly, simple-hdf-server might not be used in
production at all, with all the data statically regenerated, but you
may want to use computation-server in the production as it performs
on-demand computation jobs that cannot be precomputed.

I chose flask instead of an approach analogous to simple-hdf-server
as that approach resulted in rather foul code and I've acquired some
flask experience meanwhile.
Lightsheet: Proof-of-concept bounding box intensity plotting functionality

This is very quick'n'dirty. Plot presentation must be improved.