OPENNLP-1792: Add docbkx plugin config to produce PDF of dev manual

[mawiesne]

What does this PR do?

OPENNLP-1792: Add docbkx plugin config to produce PDF of dev manual

• modernizes xml files of the OpenNLP dev manual to use Docbook dtd in version 5.x
• adds plugin configuration to produce the PDF as separate outcome
• adds xsl file for customization of the layout of text in the PDF
• adds hyphenation support for PDF version
• introduces specific profiles for html, pdf, and epub3 targets of the dev manual
• fixes inconsistencies in dev manual's structure (duplicate ids...)
• fixes 'informaltable' column counts, mainly in cli.xml
• fixes missing inlinemediaobject for parsetree1.png image include causing trouble during epub3 generation

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