Partially revert "Web: remove duplicate information on job info page"

This partially reverts commit 2af7ee04b3f7de09a3db0433434ccc1aa5044b9c.

With Jinja 2.7 the template can map an attribute from a list of
objects, so it was not necessary to invert the obs_info data
structure.
Web: return date to obs section of job info page

The observation numbers in the observation info section
will be more useful when accompanied by the associated date.