[6.x.x] Adds missing OxygenXML libs

[adamretter]

Backport of #215

This PR Closes#209 which states:

Check datasource configuration. Could not instantiate: ro.sync.db.nxd.exist.ExistSession due to: java.lang.NoClassDefFoundError: xyz/elemental/mediatype/MediaType

Thanks to @adamretter suggestion adding the missing libs to exist-core\src\main\java\org\exist\webstart\JnlpJarFiles.java should fix the connection.

[codacy-production]

Not up to standards ⛔

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