Several places that use ui.configlist, predominantly in authentication
scenarios need to interface with systems that can contain spaces in usernames
(e.g. when client certificates are usernames, or Windows usernames).
This changeset introduces a parser that supports quoting of strings, and
escape quotation marks that get decoded into a single quotation mark that
adopts the usual behavior one would expect from quoting strings. The Python
library shlex module is not used, on purpose, as that raises if it cannot
match quotation marks in the given input.
