Add logo support for the endpoint badge and refactor logo functions (#2796)

lib/badge-data.js

lib/badge-data.spec.js

lib/load-logos.js

lib/load-simple-icons.js

lib/logo-helper.js

lib/logos.js

lib/logos.spec.js

lib/svg-helpers.js

lib/svg-helpers.spec.js

services/base.js

services/base.spec.js

services/github/github-pull-request-check-state.service.js