ESourceWebdav: Add "resource-query" property.

ESourceWebdav: Add "resource-query" property.

Retain the query portion of a WebDAV URI, and update migration to
preserve it from the old XML-based ESource URIs.

Also reimplement the "soup-uri" property.  Using bi-directional property
bindings from one property to many properties results in feedback loops.
Instead, listen for "notify" signals from URI component properties and
emit a "notify::soup-uri" signal, but don't actually update the internal
SoupURI until a copy is requested.

This makes Facebook birthday calendars work again, which has the form:
webcal://www.facebook.com/ical/b.php?uid=<<UID>>&key=<<KEY>>