Feat/skywire app example

[ersonp]

Did you run make format && make check?

Fixes #

Changes:

How to test this PR:

1. On machine A build with make build-examples
2. On machine A run ./skywire-cli config gen -irtm to create a example-server-app entry in config
3. On machine A start the visor and start the example-server-app from UI or CLI
4. On machine B build with make build-examples
5. Start the visor
6. Register the external app example-client-app by ./skywire-cli visor app register -a example-client-app
7. Copy the proc key printed by the above cli and use it in ./app/example-client-app -procKey <proc-key> -addr <visor-a-pk:45>
8. Check the logs of the binary for a hi reply message
9. Deregister the proc after it's use with ./skywire-cli visor app deregister -k <proc-key>

Skyproxy

1. Start a visorA from this branch on remote
2. Start the example http app with go run ./example/http-server/server.go this will start the app on port 9080
3. Start a visorB from this branch on local
4. Run ./skywire-cli skyproxy connect <remote-pk> --remoteport 9080 --localport 9000
5. Open localhost:9000 on local and access the example http server running on remote
6. List the open proxies with ./skywire-cli skyproxy ls
7. To stop the proxy use ./skywire-cli skyproxy disconnect <id> (get the id from the above step)

[0pcom]

revisions I've just pushed

[0pcom]

looks good, nicely done

I will come back before the release and update any documentation which needs tobe updated. I've updated the main README for skywire-cli but I see there are other docs included here as well.