Change Timecard back from an abstract model.

Prevents validation errors. Never need Timecards directly, so it would
be nice to figure out ForeignKeys and change this back.
Commit before attempting to upgrade Django.
Add view and associated code for user summary.

Tweak view template. Introduce DisplayInformation class, which houses
common attributes/logic between data for summary list, summary table,
and whatever else may be introduced. Various other edits.