Add support for custom geometry output formatters in templates. The default formatter is WKT and is the one that is used by default when using the normal {$model->GEOMPROPNAME} syntax. Using a custom formatter can be achieved using the expression of the form {$model->GeometryAsType("GEOMPROPNAME", "FormatterName")}

There is currently only one formatter: GeomWKT to output geometry as WKT.