Collective.mtrsetup

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- Nothing changed yet.

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- Add Plone 5.1 support by replacing the old PloneTestCase with plone.app.testing [mathias.leimgruber]
- Drop Plone 4.1 support [mathias.leimgruber]

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- Remove z3c.autoinclude:includeDependencies. [jone]

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- The mimetype values should be string not unicode,
especially for the icon_path
[ale-rt]

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- Fixed mimetype icon URLs to be relative
and not absolute from root
[keul]

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- Added xmind mimetype in example profile.
[thomasdesvenain]