Calculate stats when the search is run

Takes data from the status facet, combines it with the `total_entries` value returned by Sphinx and turns them into percentages for current (aka "In Progress"), refused and approved. These new values are returned, alongside a might-be-useful copy of `total_entries` (renamed `total_results`) as the `stats` property of the `HampshireSearch` instance.

Closes #42
Closes #44

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