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.
Fixed windows ANGLE bug
Created subscriptions for emails
Created corresponding subscription to server's subscriptions.js
Updated mainview.
Made set default gain and gamma only visible to admins
Removed image visibility restriction
Removed ability for non-admins to make annotations
Updated about link to link to GitHub
Made folders not draggable for non-admins
Restricted folder adding to admin
Restricted removing annotations to admins
Merge branch 'master' into production