store expiry with cert fingerprints

We used to store the creation date but this way it's easier to query for non expired certs
Identity view cert_fingerprints_by_expiry

Also move complex identity views into js designs.
Includes test.

Here's how you would query it from outside rails:
```
$ curl
'localhost:5984/identities/_design/Identity/_view/cert_fingerprints_by_expiry?startkey="2014-07-05"'
{"total_rows":4,"offset":1,"rows":[
{"id":"6c9091d4f13eaeaa6062c9d0528fd34d","key":"2014-07-05","value":"fingerprint"},
{"id":"6f3aa93828b4f6978d551f2623b9d103","key":"2014-07-05","value":"fingerprint"},
{"id":"b6cafacfa65042679691cd5065fb19e3","key":"2014-07-07","value":"fp"}
]}
```

Note that the expiry will be used as the key. So you should use the
current data (or yesterday) as the startkey to get all fingerprints that
have not expired yet.

The fingerprint itself is in the value. No need to include docs.
fix tests and simplify time calculations
minor: fix typo in load_views

It removed most of the reduce functions... really not what we wanted
allow querying for the expiry of a particular fingerprint
Merge pull request #175 from azul/feature/view-for-valid-certs

Feature/view for valid certs