Allow users to import, export, and share custom gamemodes

[MoralCode]

Users should be able to include their favorite gamemodes (like hallmark bingo) either by URL as hosted on an external server or uploaded with a manual file.

This would be a great way to facilitate sharing and resharing of board tile definitions and allow for the growth of a community for creating bingo boards for more specialized topics that arent as universally useful.

Some TODOs:

• allow importing a board definition (generically) in addition to the stock one
• allow importing boards from an external URL
• allow importing boards from a file upload
• allow specifying boards to auto-import from the web via a URL query parameter
  • maybe show a confirmation dialog so this is harder to use for malicious code execution in case there is a vulnerability
• allow users to download the definitions for a given gamemode to share
• allow users to specify additional metadata to enable better tracking of the source of a gamemode and sharing/updating/contributing back
  • gamemode version number or other universally unique identifier based on the contents of the gamemode (tiles .etc) so versions can be identified
  • canonical source URL for fetching updates to tiles
  • author information
  • license/permitted use information
• add a page that allows users to create/edit their own board definitions
• create a JS library to abstract away the board object schema

[MoralCode]

maybe this could also be done via pastebin or github gists?

[MoralCode]

this may require having a library, website, or some piece of code to validate the game boards so people can check if they will work.

user generated content could potentially get pretty terrible security wise, but maybe its fine with just a client-side-only app?

[MoralCode]

having a specification for the (json based???) format and/or a builder tool to create/import (and dedup??? #9 ) these boards might be super cool.

Maybe some kind of tool where you can upload existing boards and it OCR's or somehow parses the bingo tiles out and generates a spec-compliant set of tiles/whatever for them.

[MoralCode]

seems like https://github.com/kbuzsaki/bingosync might be able to benefit a lot from a spec like this given how many requests for new boards they have