Plone 4.0 compatibility. Travis tests for 4.0 | 4.1 | 4.2 | 4.3

See https://travis-ci.org/silviot/plonetheme.bootstrap/builds/6582238
And
http://plonetheme.bootstrap.s3.amazonaws.com/builds/6582238/4.0/robot_log.html
http://plonetheme.bootstrap.s3.amazonaws.com/builds/6582238/4.1/robot_log.html
http://plonetheme.bootstrap.s3.amazonaws.com/builds/6582238/4.2/robot_log.html
http://plonetheme.bootstrap.s3.amazonaws.com/builds/6582238/4.3/robot_log.html

Unfortunately artifact archiving will stop working when this is moved to the collective repo.
I'll come up with something.