Long live QUrlQuery

Long live QUrlQuery

This class is meant to replace the QUrl functionality that handled
key-value pairs in the query part of an URL. We therefore split the
URL parsing code from the code dealing with the pairs: QUrl now only
needs to deal with one encoded string, without knowing what it is.

Since it doesn't know how to decode the query, QUrl also becomes
limited in what it can decode. Following the letter of the RFC,
queries will not encode "gen-delims" nor "sub-delims" nor the plus
sign (+), thus allowing the most common delimiters options to remain
unchanged.

QUrlQuery has some undefined behaviour when it comes to empty query
keys. It may drop them or keep them; it may merge them, etc.

Change-Id: Ia61096fe5060b486196ffb8532e7494eff58fec1
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>