Handle JSONP correctly

The JSONP wrapper should not be cached by RABL. The workaround is described here: https://github.com/nesquena/rabl/issues/548. Also added tests that behave as expected.

This closes https://github.com/articlemetrics/alm-report/issues/35. 
Line is too long. [131/80]<br>Never use `unless` with `else`. Rewrite these with the positive case first.