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 absolutely see the utility in allowing the bucket name to be configurable from a development perspective, and I also understand the interest in having deterministic bucket names based on time scales; however, for this particular use case, it is my current understanding that the client (Firefox) will expect a given URL with only one dynamic element: the (so-called) UUID.  This is the reason why I originally stated "The name of this bucket is not dynamic".

For reference, according to the [Amazon documentation](https://aws.amazon.com/s3/faqs/) there are no limitations on bucket size:
> The total volume of data and number of objects you can store are unlimited.

In any case, I agree that it's a good idea to make this configurable.  I don't know if it should be auto-generated, however - that's seems like something we'd need to speak to the consumer (read: @bsmedberg et al.) about.