Fixed issue with Web Docker image not getting proper environment variable substitution

As ReactJS does not seem to support reading environment variables from Docker runtime variables, we'll pull it instead from buildtime.
Also added copying of nginx config file in the Dockerfile
Modified API Dockerfile to accept WebUri for CORS, also removed duplicate setting of CORS in Program.cs

Web/nginx.conf

@@ -0,0 +1,9 @@
+server {
+  listen 80;
+  server_name localhost;
+  root /usr/share/nginx/html;
+  index index.html;
+  location / {
+    try_files $uri $uri/ /index.html;
+  }
+}