Grokcore.viewlet

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* Make package comply to zope.org repository policy.

* Update functional tests to use Browser implementation of zope.app.wsgi
instead of zope.app.testing.

* Reduce dependencies (zope.app.pagetemplate no longer necessary).

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* Dropped the dependency on ``zope.app.zcmlfiles``.

* Cleaned the code to remove unused imports and ensure the pep8 syntax.

* Updated tests to have a return value consistency. The
grokcore.viewlet viewlet manager implementation requires viewlets to
return unicode strings. Now, viewlets return unicode strings in the
test packages.

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* Define test requires.

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* Reverted the use of grokcore.view.CodeView. We now require
``grokcore.view`` 1.12.1 or newer. As of ``grokcore.view`` 1.12, the
CodeView/View separation has been undone.

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* Remove the reference to the grok.View permission that is no longer in
grokcore.security 1.2

* Use the grok.zope.org/releaseinfo information instead of our own
copy of ``versions.cfg``, for easier maintenance.

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* Adapted tests to new grokcore.view release: switched from View to CodeView.

* Add grok.View permissions to functional tests (requires grokcore.security
1.1)