Made Throwables show their errors more completely in QLog

With the exception of StackOverflow, which is dangerous.
Fixed sorting on results of _foreachProperty

_sort was broken because PropAndValProp didn't have doSerialize()
defined.
.3y285jw and then some: rewrite of Model rendering

Bigger change than originally planned: check all these details for the
release notes.

Main change: introduced the Model View property.  This determines how to
render a Model, separately from Default View, and is an old request from
Eric.  If not specified, a Model will simply show the default rendering.

Added the _rawVal function, which is mainly interesting so far because
it turns any Text value into a raw HTML code block instead of performing
any further QL processing on it.

Rewrote the default rendering of all Things.  Broadly similar to before,
but uses _rawVal to display the raw text.  (This might want to get
changed to only use _rawVal on models.)

Pulled XML escaping out of BaseParsers into XmlHelpers, so that we can
use it more generally.