Tk#411 - 3.3: Use of explicit uom within SE Styles

http://tracker.deegree.org/deegree-services/ticket/411

This feature is part of the OGC Symbology Encoding standard.
With this enhancement is possible to overwrite the unit of measure (attribute "uom") for symbolizers setting the value for "stroke-width" or for the other options using "px" after the number. Ex.:

```xml
<se:PolygonSymbolizer uom="mm">
    <se:Stroke>
        <se:SvgParameter name="stroke-width">3px</se:SvgParameter>
    </se:Stroke>
</se:PolygonSymbolizer>
```

I implemented this feature for the next symbolizers and options:

PolygonSymbolizer: Stroke-width - PerpendicularOffset - Gap;

LineSymbolizer: Stroke-width - PerpendicularOffset - Gap;

TextSymbolizer: LinePlacement: PerpendicularOffset - PointPlacement: Displacement