Allow searching of old and current elections

[frabcus]

Have a way to handle multiple elections, and let the search apply over them.

Perhaps only have browse for old elections, as mapit won't necessarily be reliable? Not sure if it is reliable or not historically.

There'll be a mode where there is no current postcode lookup, when there is no active upcoming election yet in YourNextMP (from our point of view we'd like there to always be a best guest list of candidates for next General Election).

In that mode though, you'll still be able to browse (or maybe lookup) for old elections.

See also #71

[frabcus]

Old elections are by download only at http://cv.democracyclub.org.uk/archive