ADD: Added feature to add additional parameters in wkhtmltopdf rendering.

Example:

export.exportConfigs.pdfExport.additionalWkhtmlParams = --footer-right "Seite [page]/[toPage]"
ADD: Added feature to add footer and header from html with wkhtmltopdf rendering.

Example:

    export.exportConfigs.pdfExport.wkhtmlHeaderHtml (
    	Some <b>Header</b> HTML Code
    )

    export.exportConfigs.pdfExport.wkhtmlFooterHtml (
    	Some <b>Footer</b> HTML Code
    )
FIX: check node instance in getDisplayValue() of TreeSelectFilter
TASK: merge