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

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