[feat] osx build templates

Makefile

README.md

branding/README.txt

branding/assets/riseup/riseupvpn.icns

branding/scripts/check-ca-crt.py

branding/scripts/generate-osx.py

branding/scripts/generate-vendor-make.py

branding/templates/makefile/Makefile

branding/templates/osx/bitmask.pf.conf

branding/templates/osx/client.down.sh

branding/templates/osx/client.up.sh

branding/templates/osx/cross-compile.txt

branding/templates/osx/generate.py

branding/templates/osx/quickpkg

branding/templates/osx/signbundle

branding/templates/osx/template-helper.plist

branding/templates/osx/template-info.plist

branding/templates/osx/template-postinstall

branding/templates/osx/template-preinstall

branding/templates/windows/generate.py