Ignore title in form in serializer to avoid TiddlerFormatError

Some time ago it was discovered that it was possible to create
tiddlers with a 'title' in the 'fields' attribute. When using
the text store this would save the title onto to disk and then
cause errors when reading the data back to create a tiddler object.

Since we've already used the title field in the form to set the
title of the tiddler we can skip over it here and avoid the
error.
release 0.11