* Fixes for E_NOTICE in workqueue:
- introduced class `Friendica\Util\Arrays` which will hold static methods for
handling arrays that cannot be done with PHP's functions, like implode() on
multi-dimensional arrays
- rewrote old-school for() loop to foreach()
* Added intial unit test with some tests on empty delimiters and/or sinle and
multi-dim array.
* Added test for for 3-dimensional arrays, thanks to nupplaphil's feedback.
