server: new backend

This CR adds a new backend based on TypeScript, Express, WebSocket and
Rollup.
To build the server:
> npm run build
To develop with dev mode:
> npm run start

GitLab: #47
Change-Id: I6cdacab14104ea67c559e3f9e892fbc1b17a022d
diff --git a/server/.eslintrc.json b/server/.eslintrc.json
new file mode 100644
index 0000000..8248d92
--- /dev/null
+++ b/server/.eslintrc.json
@@ -0,0 +1,3 @@
+{
+  "extends": ["../.eslintrc.cjs"]
+}