Errors and warnings when quads in, triples out

[afs]

GitHub issue resolved #1873

Changes to the command line:

• warn if inputs include quads but output is triple only.
• warn if inputs generate quads but output is triple only (stream default graph only)
• error if inputs generate quads but formatted (i.e. buffered) output is triple only

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• Tests are included.
• Documentation change and updates are provided for the Apache Jena website
• Commits have been squashed to remove intermediate development commit messages.
• Key commit messages start with the issue number (GH-xxxx or JENA-xxxx)

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See the Apache Jena "Contributing" guide.