Add first version of u-track downloads page (rebased onto develop)



This is the same as gh-61 but rebased onto develop.

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Similar to #58, this PR provides the framwork for generating a downloads page for the U-Track partner project. The corresponding jobs should be http://ci.openmicroscopy.org/view/Consortium/job/U-TRACK-release/? and http://ci.openmicroscopy.org/view/Consortium/job/U-TRACK-release-downloads.

/cc @hflynn