Deployer v2 -- Simpler deploy configs, OS X fixes, new Windows Travis bot

The current Deployer setup is exceedingly complicated to configure, so I sought to simplify it. The motivation is to lay the groundwork for Linux AppImage per this GitHub issue. By doing so, I rip out support for Debian packages, clean cruft, and upgrade things.

See this Wiki page for details on the config changes.

Changes

Builds in general

• Windows: New Travis bot for CMAKE. Builds on GCC 10. Enabled CCache and MSYS2 package cache (it's faster to install from scratch).
• OS X: Upgraded to Xcode 11.5. Enabled CCache. Switched from Homebrew to MacPorts, so we can build all dependencies from source.
• Jobs: No more Launchpad deployer bots. No more separate deployer bots. Three test bots are designated as deployers, provided they meet the trigger conditions.
• CPU targeting: The deploying bots target -march=nocona -mtune=haswell to optimize game performance. See !454 (closed) for the rationale.

Deployment-specific

• Deploy targets: New GitHub Releases target. DPUT is dummied out.
• Triggers: Deployer is now on-by-default for release tags, provided the necessary GitHub/FTP auth tokens. Branch name and commit message triggers can be configured, as well as force on/force off for branches.
• AppVeyor: Removed deployer because it's made redundant with Travis Windows.

Notes

Depends on cmake-adjustments !991 (closed).

See these build logs:

• Deploying build
  • Package build downloads
• Non-deploying build
• OS X, before cache: 44 minutes
• OS X, after cache: 11 minutes
• Windows: 7 minutes
• Linux: 3 minutes