Replace the default plone add site button behavior

[maethu]

As described in http://stackoverflow.com/questions/39167185/avoid-creation-of-plones-default-content (comment).

It is possible to unconfigure the default behavior and add a custom one. Example: https://github.com/plonegovbr/brasil.gov.portal/blob/master/src/brasil/gov/portal/browser/plone/overrides.zcml#L11

pros:

• Only one button
• Remove patch (for further compatibility)

cons:

• Do we want only one button?

[jone]

For creating a standard-Plone site I still use the default add-site button sometimes, even when inflator is available, e.g.:

• if I want to compare default configurations in local development
• if I want to build a specific setup, which is not covered by any available inflator bundle
• when developing ftw.inflator, which does not configure a standard bundle

So I'd probably still keep both buttons in the ZMI, but only the inflator-Button in the index-View.