Add implode method to Collection class and Query Builder

This makes it easy to glue values or column or key inside a collection or a DB result set together.

Signed-off-by: Dries Vints <dries.vints@gmail.com>
Merge pull request #1544 from driesvints/feature/collection-implode

Add implode method to Collection class and Query Builder
Cleaning up some code.
Merge branch '4.0'