Support Read Status for MMS

[efullea]

Messaging API supports handling delivery status for MMS messages. Equivalent support for read status should be added.

[airpingu]

Summarize the proposed changes for the Mozilla Messaging APIs to support MMS Read Report at [1], which is already in agreement with Eduardo and others. W3C can support the features in a very similar way.

[1] https://groups.google.com/forum/?fromgroups&hl=en#!topic/mozilla.dev.webapi/cowOmwquJts

[airpingu]

Updated: https://groups.google.com/forum/#!msg/mozilla.dev.webapi/cowOmwquJts/eEs3jIXnnPgJ

[efullea]

See Pull Request #85