Improves the rendering of labels in polygons

[lgoltz]

If the requested bounding box in a GetMap request splits the geometry feature into a multpolygon (e.g. a 'banana'-geometry into the two ends of the 'banana') the label is rendered in the center of the original geometry, which may be somewhere outside the geometry (e.g. between the two ends of the 'banana').

This pull requests fixes this by calculating points into the visible parts of the geometry in the map if auto="true" is configured.

Example

<?xml version="1.0" encoding="UTF-8"?>
<FeatureTypeStyle
    version="1.1.0"
    xmlns="http://www.opengis.net/se"
    xmlns:wupp="http://www.deegree.org/app"
    xmlns:ogc="http://www.opengis.net/ogc"
    xmlns:sed="http://www.deegree.org/se"
    xmlns:deegreeogc="http://www.deegree.org/ogc"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.opengis.net/se http://schemas.opengis.net/se/1.1.0/FeatureStyle.xsd http://www.deegree.org/se http://schemas.deegree.org/se/1.1.0/Symbolizer-deegree.xsd">
    ...
    <Rule>
        <TextSymbolizer>
            <Label>
                <ogc:PropertyName>app:label</ogc:PropertyName>
            </Label>
            <Font>
                <SvgParameter name="font-family">Arial</SvgParameter>
            </Font>  
                         <LabelPlacement>
                <PointPlacement  auto="true">
                    <Displacement>
                        <DisplacementX>0</DisplacementX>
                        <DisplacementY>0</DisplacementY>
                    </Displacement>
                    <Rotation>0</Rotation>
                </PointPlacement>
            </LabelPlacement> 
            ...
        </TextSymbolizer>
        ...
    </Rule>
</FeatureTypeStyle>