improve(docker): support multiple API URLs option (#4044)

The API_URLS environment variable can be used to run the Docker image with multiple urls.

Example:
docker run -p 80:8080 -e API_URLS=[{name:"First API", url:"http://firstapiurl"},{name:"Second API", url:"http://secondapiurl"}] swaggerapi/swagger-ui

Dockerfile

@@ -5,6 +5,7 @@ MAINTAINER fehguy
 ENV VERSION "v2.2.10"
 ENV FOLDER "swagger-ui-2.2.10"
 ENV API_URL "http://petstore.swagger.io/v2/swagger.json"
+ENV API_URLS ""
 ENV API_KEY "**None**"
 ENV OAUTH_CLIENT_ID "**None**"
 ENV OAUTH_CLIENT_SECRET "**None**"