Feature/activate poltergeist for rspec

[ulferts]

No description provided.

[oliverguenther]

Even the up-to-date PhantomJS 2.1 has significant issues with flexbox.

ariya/phantomjs#14365
ariya/phantomjs#12367

It appears that the workaround from the first issue (adding Safari >= 4) does help somewhat. Let's see what breaks!

[oliverguenther]

./spec/features/groups/group_memberships_spec.rb:86 appears to fail because the click is sent to the other button next to it. The triggered link is the remove button, but the coordinates response of PhantomJS with debug enabled return the button left to it. The screenshots confirm, that instead of removing the row, the row is turned into edit mode.

[oliverguenther]

While this is a valiant effort, after the experiences made here trying to fix the tests, and the results from the cukes running on dev, I suggest we stop this effort. PhantomJS appears to have lots of bugs that happen to be occurring on our application and issues with Flex.

I suggest to revert the cuke change here: #4946