New rackspace auth identity filter

For grins, I reimplemented the poorly named content-identity filters for Rackspace Identity.

I called it the "Rackspace Auth Identity Filter" so it would fit along the lines of the "IP Identity" filter, which uses your IP address as your user. 

This uses Rackspace Authentication parsing logic to get the username out of a myriad of responses.

It uses the builtin scala XML parsing library to read XML responses, and it uses play-json to parse the JSON responses in a similar manner.

Open to comments, but I think it's substantially less confusing than the existing filters, and it's got way less dependencies. The code is cleaner, easier to understand (even though it's in scala).

I think we can probably ship this as part of any release of Repose, not just the latest one.
That read limit is there on both of the other identity filters. It stops the processing after a certain number of bytes. 

On September 29, 2014 3:49:51 PM EDT, Adrian J George III <notifications@github.com> wrote:
>> +                <html:p>If this element is specified, the filter
>will attempt to parse out a payload for the identity
>> +                    v2.0 contract (either json or xml) and extract
>the username. Group will be as configured, or the
>> +                    default of PreAuth. The default quality applied
>to the header will be 0.6
>> +
>> +                    If you want to have different groups for 1.1 and
>for 2.0 you need to specify them, else they will
>> +                    use the same default.
>> +                </html:p>
>> +            </xs:documentation>
>> +        </xs:annotation>
>> +
>> +        <xs:all>
>> +            <xs:element name="group" type="xs:string" minOccurs="0"
>maxOccurs="1" default="Pre_Auth"/>
>> +            <xs:element name="quality" type="xs:string"
>minOccurs="0" maxOccurs="1" default="0.6"/>
>> +        </xs:all>
>> +
>> +        <xs:attribute name="content-body-read-limit"
>type="xs:positiveInteger" use="optional" default="4096">
>
>What?
>
>---
>Reply to this email directly or view it on GitHub:
>https://github.com/rackerlabs/repose/pull/1124/files#r18178356

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