SDL: Fix missing header

This fixes linux and mingw builds.

Port citra-emu/citra#4950: "Add FPS to SDL title bar"

[crypto] Use IsAllZeroArray helper function

externals: Track mainline zlib as a submodule

Likewise, we also only want to link in the libraries that we actually
make use of (so we don't need to worry about linking in test targets).

We don't need to depend on a custom fork for this. We can add the
library as is, and then make it excluded from the ALL target, so we only
link in the libraries that we actually make use of.

Port citra-emu/citra#4004: "qt_themes: add two colorful themes"

bcat: Implement BCAT service and connect to yuzu Boxcat server

ci: Add windows MSVC builds to patreon and mainline pipelines

ci: Iterate through GitHub pages for pull requests

Signal styleset changes at a better time

Remove AppVeyor status from the readme.md