Rename backend server to headlamp-server

Plugin improvements

So the assets are all inside the dist/main.js

I think before because two loaders were being used images were not
displaying properly.

Using style-loader and css-loader headlamp plugins. The styles are
packed into the output main.js file, not as separate css files.

It's only meant to check the typescript for issues not generate files.

github: Fix golang version to one version

The former name was too generic, which made it difficult to spot, and
could clash on Windows as well.

This patch renames it as headlamp-server but keeps as /headlamp/server
symlink in the container image, for backward compatibility.

plugins: Show how to use styles inside a plugin

Fix plugin imports again

The include path was relative to headlamp-plugin in node_modules, so
it didn't work when just extending the plugins-tsconfig.json file.
This change set the path to be the plugin's own top directory + src
files, so it allows plugins' tsconfig to simply extend the mentioned
shipped tsconfig instead of having to override the "includes".

We want to allow an import like:
import { makeCustomResourceClass } from '@kinvolk/headlamp-plugin/lib/K8s/crd';

but the plugins-tsconfig.json was not resolving these paths correctly
due to a mix of legacy/invalid type path and also the baseURL being set
to "." which made the paths be resolved in the headlamp-plugin module
in module_nodules and not from the plugin's top dir.

Headless app fix

Fix default class names

Docs had been created without a plugin that renames the default
exports, so a lot of classes were names as default.

This patch uses the "typedoc-plugin-rename-defaults" package which
renames the default exports, otherwise e.g. classes that are part of
the lib/k8s modules would be exported as simply "default".

Plugin changes

Bundled app plugins

frontend: Add networkpolicy API

We would be needing the networkpolicy API for the security advisor
plugin. This patch adds the required API for it.

Allow listing resources per namespace