bug 1066058; add Support Reason API crashstorage type

*Preamble: This PR is primarily submitted for discussion purposes (I expect more work to be necessary).*

This adds the `SupportReasonAPIStorage` class which is a sub-class of `BotoS3CrashStorage`; functionally speaking, the former is basically a *highly lossy* implementation of the latter.

cc @twobraids 
I would suspect that a single bucket for all crashes for all time is not appropriate.  We'll eventually have a need for aging buckets of support reasons out of the system.  This will be especially true when we hit 100% processing.  Maybe daily, weekly, or monthly buckets would be more appropriate.

Try the configurable bucket name as prefix to the dated bkcet name like this:

```python
def _create_bucket_name_for_crash_id(self, crash_id):
    return "%s_%s" % (self.config.bucket_name, crash_id[:-6])
```
If we really want to be clever, make the daily, monthly, yearly part be configurable, too.