Implement charges "holding" things

[karlwilcox]

The bulk of the required code already exists (see "holding" in the parser, and use the same technique as for "crowned" in which we locate an empty SVG rectangle with id "holding" and transform the charge to fit within it)

The (much) bigger part is modifying all the charges that could conceivably hold things so that the SVG "holding" rectangle is placed in the appropriate location.