Related to: 495e46d4

This can be removed for PHPLIB-87 once PHPC-274 is resolved.

This removes some copypasta from existing Database and Collection code.

Also change "read-only" language to "immutable".

This obviates the need to handle stdClass instances within the results.

PHPC-224 consolidated the Result and Cursor classes into one. Additionally, PHPC-203 changed toArray() to return iterator_to_array($this) instead of only the first result document. For commands, this means we need to extract the first element in toArray()'s return value.