Since the update of `bastik` the PDF servlet didn't work anymore.
Problems:
- No PDF UnitTest existed
- Pom dependency `org.apache.xmlgraphics.batik-all` change nearly every dependency to `optional` starting with version `1.15`, hence some important dependencies like the SVG converter were missing
- `DiagramResponse.CONTENT_TYPE` had no mime type value for PDF
Changes:
- add PDF UnitTest
- remove `batik-all` dependency and only include the dependencies PlantUML requires for the PDF generation:
* batik-dom
* batik-svgrasterizer (includes batik-dom)
* batik-svggen
* fop
- remove own `DiagramResponse.CONTENT_TYPE` mapping and use `FileFormat.getMimeType()`
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