Catch AccessDeniedExceptions

## Catch AccessDeniedExceptions

### Acceptance Criteria
1. When a user visits an endpoint but is restricted from access via access rules, the AccessDeniedException is caught before it gets to Silex.
1. The Exception is caught and simply turned into a 403 JSON response with the following body:

```
{"error":"Access Denied"}
```

### Tasks
- Catch AccessDeniedExceptions in `Synapse\Application\Routes` and return the JSON response.