Refactor robot tests to use p.a.robotframework and support Sauce Labs

@tisto

Possible issues with this if other packages have been referring to CMFPlone robot testing resources (I'm not aware of, but if is, these can be reverted):

- This will rename PRODUCTS_CMFPLONE_ACCEPTANCE_TESTING -layer to PRODUCTS_CMFPLONE_ROBOT_TESTING (I think that Barcelona testing sprint came to conclusion that it is misleading to call robot tests acceptance tests.)
- This will rename keywords.txt to common.robot (because it does not contain only keywords).

Tests are still running at:

- https://jenkins.plone.org/view/Sauce%20Labs/job/plone-4.3-python-2.7-robot-datakurre/
- http://saucelabs.com/u/plone

Most probably there are still issues with IE at least, but most probably those issues did exist already before this refactoring.