Fix compile on Java 8.

The original code was causing javac to throw an AssertionError. Working
around the labelled break (by using a flag) seems to fix this fine.
Trying to minimize differences against the original code.
jai: Remove commented-out jj2000 breaks
Use latest/bio-formats5.1 redirects
Install Sphinx using pip instead of apt-get

The Travis build seems to be failing on a bug which has been fixed in
the 1.2.2 version of Sphinx that we currently use in production
Fix downloads link in sidebar to use new redirect
Merge pull request #1270 from sbesson/latest_redirect_5.1

Use latest/bio-formats5.1 redirects
Merge pull request #1261 from rleigh-dundee/jj2000-jdk8

jj2000: Fix compile on Java 8