DiscordInt 1.1: Two way Discord bridge + admin channel commands + join/leave notices

[KNAPPE0]

Short and concise description about my pull request:

• Upgrades the original DiscordInt 1.0 draft into the full 1.1 Discord integration. This pull request focuses only on Discord related functionality.

TODOs:

• - I confirm this PR is at its final form and will not receive more pushes to it unless modifications are required.
• - I confirm this PR has been previously tested by me and has no apparent issues.
• - I confirm this PR is complying with this project's Contribution Guidelines.
• - I confirm this PR is complying with this project's Syntax Ruleset.

Longer / More informative description about what my pull request does:

• Adds a dedicated Discord bridge with two way chat relay between Discord and the in game chat, optional admin channel command execution, and join/leave announcements. Improves reliability and server safety that has guarded calls, outbound queuing, batching and includes a basic rate limiting, plus safer sanitization to help prevent unwanted mentions and or spam from occuring.