Update plone/app/testing/selenium.rst

Selenium and transactions bit added
Update plone/app/testing/selenium.rst

Reordered the long bit to its own subsection with an example
Update plone/app/testing/selenium.rst

More structure and pitch about Selenium
Allow testing with non standard port. Allows running multiple test suites in parallel
Update changelog.
Preparing release 4.2.1
Back to development: 4.2.2
Install PythonScripts package
Update README.rst

How to enable workflow
Add [robot] extras for requiring dependencies for Robot Framework tests
sphinx.cfg added.
gitignore updated.
Initial sphinx documentation added.
Include README.rst in sphinx.
Whitespace.
Whitespace.
Whitespace.
Merge pull request #1 from plone/datakurre-robot-extras

Add [robot] extras for requiring dependencies for Robot Framework tests
Prepare 4.2.2 release.
Merge branch 'master' into simpler-helpers
Merge branch 'master' into simpler-helpers