Add grpc-gw usage example

[generalhenry]

ref: #425

Add a example of using the amplifier-gateway api to build a ui

To test:
./shrink.sh local
amp pf start --local
cd examples/ui
./deploy.sh
open http://www.gw-ui.local.atomiq.io/stacks/

[chrisccoy]

👍 works like a charm.

[chrisccoy]

FYI- You may get a protobuf error:

Error during: amp up, reason: rpc error: code = 2 desc = proto: can't skip unknown wire type 7 for stack.Stack

if you do not perform a make install prior to the deploy step

[JosephGJ]

LGTM. Had to open link in a chrome window rather than safari.

[generalhenry]

re: safari
I built it using new browser features, and safari is missing one of them (fetch) it's easy to polyfill but for now the browser support matrix is [chrome 55+] though it should also be working in firefox, opera and edge. (safari is sadly the new IE)

[bquenin]

LGTM, tested on linux with Chrome 55