integrate martin's stremio-addon-proxy + backup snapshots

[Ivshti]

Replace NGINX with https://github.com/MartinKavik/addon_proxy_1/

These considerations apply:

• needs a way of autoconfiguring, see #11
• short timeouts, e.g. 5-6 seconds, for security purposes (to keep slow services from screwing up the entire system)
• cron to backup the whole sled database every 24 hours, therefore snapshotting addon cache

Keep in mind, the proxy brings the following advantages:

• smarter cache: keeps serving responses for some configurable amount after they've expired if the origin is down
• smarter validation: only allows addon requests
• perhaps better performance?