hgweb: move HTTP content types out of header templates
This removes the ability for templates to add custom HTTP headers, which can
easily be re-added if someone needs it. Thanks to asak for repeatedly reviewing
this patch and helping to iron out the quirks.
default = 'changelog'
feedupdated = '<updated>#date|rfc3339date#</updated>'
mimetype = 'application/atom+xml; charset={encoding}'
header = header.tmpl
changelog = changelog.tmpl
changelogentry = changelogentry.tmpl
filelog = filelog.tmpl
filelogentry = filelogentry.tmpl
tags = tags.tmpl
tagentry = tagentry.tmpl