Add an optional extension profile to disable existing Plone transforms

[lukasgraf]

Existing Plone default transforms may cause error messages in logs like the ones shown below, even though ftw.tika already provides a path for creating text/plain from those MIME types, and those transforms aren't needed any more.

I therefore suggest we create an optional profile that can be installed / depended upon that unregisters those transforms.

2015-09-01T11:34:58 ERROR PortalTransforms Cannot register transform lynx_dump, using BrokenTransform: Error
 Unable to find binary "lynx" in /home/zope/bin:/home/zope/perl5/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin
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2015-09-01T11:34:58 ERROR PortalTransforms Cannot register transform pdf_to_html, using BrokenTransform: Error
 Unable to find binary "pdftohtml" in /home/zope/bin:/home/zope/perl5/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin
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2015-09-01T11:34:58 ERROR PortalTransforms Cannot register transform pdf_to_text, using BrokenTransform: Error
 Unable to find binary "pdftotext" in /home/zope/bin:/home/zope/perl5/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin
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2015-09-01T12:02:27 ERROR PortalTransforms Cannot register transform lynx_dump, using BrokenTransform: Error
 Unable to find binary "lynx" in /home/zope/bin:/home/zope/perl5/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin
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2015-09-01T12:02:27 ERROR PortalTransforms Cannot register transform pdf_to_html, using BrokenTransform: Error
 Unable to find binary "pdftohtml" in /home/zope/bin:/home/zope/perl5/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin
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2015-09-01T12:02:27 ERROR PortalTransforms Cannot register transform pdf_to_text, using BrokenTransform: Error
 Unable to find binary "pdftotext" in /home/zope/bin:/home/zope/perl5/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin