Reply position results in extra needless queries

[johnjamesjacoby]

When trying to get the position of a reply in a topic, we're currently querying for topic children for each reply in a loop. This results in direct database hits for each iteration. The queries are cached at a lower level, but for as often as this is called, this can be architected better.

I propose using menu_order in place of bbPress 1.x's post_position property.

[johnjamesjacoby]

(In [3934]) Reply Position Improvements:

• Add _update_ and _raw functions for reply positioning.
• Use these functions through-out the codebase as needed.
• Maintains the existing bbp_get_reply_position() behavior, so it's backwards compatible.
• Fixes #1840.