hgweb: add phase to {changeset} template
It's pretty surprising phase wasn't part of this template call already.
We now expose {phase} to the {changeset} template and we expose this
data to JSON.
This brings JSON output in line with the output from `hg log -Tjson`.
The lone exception is hweb doesn't print the numeric rev. As has been
stated previously, I don't believe hgweb should be exposing these
unstable identifiers. (We can add them later if we really want them.)
There is still work to bring hgweb in parity with --verbose and
--debug output from the CLI.