Fix Travis on 1.5.x branch

[mauritsvanrees]

See what goes wrong in the Travis jobs for PR #78:

• Plone 4.3 fails because of some weird problem installing configparser for code-analysis. Fixed by installing and running code-analysis only on Plone 5.2 in a separate job.
• The others pass, but at the end we do a few commands for coveralls, but half of the commands fail, leading to a blank coveralls report that apparently defaults to showing 67 percent. Solved by removing the coverage code from the Travis yaml file. We can improve that on master if we want.

[mauritsvanrees]

This fails with ImportError: cannot import name decode_utf8, which is what PR #78 fixes. I will close the current PR and rebase the other PR on top of this branch.