Create staticCms.ts to serve the CMS without Lume site building

[revgum]

Re: Issue #3

A static CMS server that could be used like so;

import cms from "./_cms.ts";
import staticCms from "https://raw.githubusercontent.com/revgum/cms/master/adapters/staticCms.ts";

const app = await staticCms({ cms });
Deno.serve({
  port: 3000,
  handler: app.fetch,
  onListen() {
    log.info("CMS server started");
  },
});

[revgum]

Unnecessary, can be implemented like https://github.com/lumeland/cms-demo/blob/main/mod.ts#L48