Add problem report totals endpoint

This endpoint allows getting summaries by day, which is useful
because it allows publishers to see which part of the site to focus
on and improve.

Request:
```
GET /anonymous-feedback/problem-reports/2014-09-24/totals
```

Response:
```
{
  date: "2014-09-24T00:00:00+00:00",
  results: [
    {
      "path": "/tax-disc",
      "total": 3
    },
    {
      "path": "/jobmatch",
      "total": 2
    }
  ]
}
```
Merge pull request #17 from alphagov/add-problem-report-totals-endpoint

Add problem report totals endpoint
Worker for pushing problem report daily totals to PP
Schedule changes and rake task for PP problem report upload
Merge pull request #18 from alphagov/upload-problem-report-totals-to-pp

Upload problem report totals to the Performance Platform