progress: move the singleton logic to the ui module
The use of a singleton for all of progress handling is debatable (because
config may vary). However this is how the extension has been doing it so far.
We move that code into the ui module because this is where is should belong when
progress is moved into core.
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state