[7.x.x] Add missing oXygenXML libs to fix

[marmoure]

This PR Fixes#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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[marmoure]

Moved to #215 due to branch name changes