Added array_column replacement for PHP < 5.5

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | ---
| Fixed tickets | ---
| Refs tickets  | ---
| License       | MIT
| Doc PR        | ---

This adds support for `array_column` to PHP <5.5. Read more about the `array_column` function in the PHP manual: http://php.net/manual/en/function.array-column.php.

I personally find it extremely useful and would like to see it in the core.