Display name for distribution series doesn't follow vendor conventions

[Matthew Paul Thomas]

1. Go to <https://launchpad.net/ubuntu/lucid>, and look at the main heading and any global navigation.
2. Go to <https://launchpad.net/ubuntu/maverick>, and look at the main heading and any global navigation.

What you see:
1. "Lucid"
2. "Maverick"

What you should see:
1. "Ubuntu 10.04 LTS"
2. "Ubuntu Maverick" (until 2010-10-10)

The convention for distribution vendors is to refer to a distribution series by its codename before release, and by its version number after release.

For example, <http://www.ubuntu.com/> prominently features "Ubuntu 10.04 LTS", and does not mention the word "Lucid". <https://wiki.ubuntu.com/CodeNamesToVersionNumbers> explains that "The names of each release (e.g., Breezy Badger, Dapper Drake) are development code names and typically for internal use only ... We don't want to use the version numbers prior to the actual release, as it increases the likelihood that a pre-release version will be mistaken for a final release. Similarly, we don't want the code names to be visible to the user once the final release has been made."

Similarly, <http://www.debian.org/> says "The latest stable release of Debian is 5.0", and does not mention the word "lenny". Conversely, <http://www.debian.org/releases/> gives a codename "squeeze" for the next version, but not a version number.

Launchpad should reflect this convention, without series maintainers having to update a field manually on release day. Specifically:
* The distribution series .displayname database field should be renamed to .codename.
* A distribution series .displayname should be a cached property, equal to its .codename when the series has not yet been released, and to its .version after it has been released.
* The main heading for a distribution series overview page should consist of the distribution.displayname plus the distroseries.displayname.

This is part of <https://dev.launchpad.net/RegistrySimplifications>.

[Stuart Bishop (stub)]

This sounds like we are not using DistroSeries.displayname where we should, instead trying to calculate the display name and doing it badly.

[Curtis Hovey (sinzui)]

We introduced named_version 18 months ago to reduce confusion about the code name and version: maverick (10.10). I propose:
  .displayname => .codename
  .named_version => .displayname
And that the new display name only shows the version with optional LTS when the series is released. We could revert the named_version rule, but that reopens the ambiguity problem when users need

We need to add a db flag to know a series is LTS (bug 547082) and we should rename the column in the db.