[Feature] Add Barter/Buyer Features

[neckkola]

Adds barter and buyer features, for ROF2 only at this time including item compensation. Would appreciate a review and others testing.

Allows for the following:
Buyer support within the bazaar (version 0 and 1) instances
Barter support including searching and buying from within and outside the bazaar

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected) As currently implemented, will break previous clients
• This change requires a documentation update

Testing

Here is a short demo of the functionality.
https://youtu.be/4d4fZsMhemQ

This has also been running in the wild for a week or so. Positive results.

Clients tested:
RoF2 Only. This will break existing buyer/barter for previous clients. Not sure if it was broadly used. I intend to enable for UF, Ti should there be demand.

Checklist

• I have tested my changes
• I have performed a self-review of my code. Ensuring variables, functions and methods are named in a human-readable way, comments are added only where naming of variables, functions and methods can't give enough context.
• [X (In progress)] I have made corresponding changes to the documentation (if applicable, if not delete this line)
• I own the changes of my code and take responsibility for the potential issues that occur
• If my changes make database schema changes, I have tested the changes on a local database (attach image). Updated version.h CURRENT_BINARY_DATABASE_VERSION to the new version. (Delete this if not applicable)

[fryguy503]

WFH has been using this a bit, all issues have been addressed so far.

[Akkadius]

Great fucking work!

I barely need to make review comments this time around. I'm so damn impressed in how much you've learned, your attention to detail and how much you've done for this community in the past year alone. Thank you for being so willing to learn, receptive to feedback, be so on top of everything and pump out huge feature gaps we've needed for such a long time.