Improve release_notes view to fix multiple bugs

Map URLs within bedrock for bug 978931

Map firefox os release notes urls to new RNA powered release_notes
view, with fallback to manual templates for 1.0.1, 1.1, and 1.2 to
support the template development for bug 978988

respect Release.is_public flag unless settings.DEV is True

Map auroranotes to RNA release_notes view

Beta notes will also work if the version # matches the version_re,
which for example 28.0b1 will, but 28.0beta will not

We no longer "fix" version numbers like 27.0 -> 27.0.0 -- this was
an artifact of data migrations that we need to fix in the nucleus
DB now that we've gotten past those migrations

The release_notes view now expects the version string to be unique per
product

mobile release notes are not yet supported, further work
will be done as part of Bug 965012.