Add view (and export) options to key entry forms

[isedwards]

The view option should allow users to select station, year and month for any given key entry form.

The data will be displayed in a table view with Export and Close buttons.

See #17 for implementation of export option.

The Close button shoud be populated with a link to the page that we should return to, e.g. /keyentry/hourly/<stationid>/<elementid>/<year>/<month>/<day>/ (see #32)