hgwebdir: read --webdir-conf as actual configuration to ui (issue1586)
This cleans up code and allows specification of values more globally. For
example, it's now possible to specify web.contact in webdir-conf for all
repositories without a specified contact set.
adding bar
adding foo
% state dump after
n 666 -1 bar
n 666 -1 foo
% status
! bar
? baz
C foo