Add gui server

[hannaeko]

Purpose

Add a basic web server to serve GUI files.

Context

Based on #434
Following a discussion in the face to face, we decided to serve the GUI from a server to allow more flexibility.

Changes

• Add a server in perl (using Dancer2)
• Template index.html to include additional resources and override default ones (for css)
• Detect browser language using the server
• Add Makefile.PL for packaging
• Update reverse proxy documentation
• Update installation doc in zonemaster/zonemaster repo
• Add service script to manage daemon
• Add example configuration and update configuration documentation
• Remove unused files (configuration, scripts, ...)

How to test this PR

Running the server:

% plackup scripts/zonemaster-gui

[hannaeko]

This is still a draft as it is not finished, but I would like some early feedback to avoid going the wrong path.

[hannaeko]

Commit 80e36dd is the relevant stuff

[hannaeko]

I still need architecture approval on this PR to finish (or change) this work.

[marc-vanderwal]

In terms of architecture, I see no issues; I agree with the choice of Dancer2.

[matsduf]

Danser will create daemon listening to http, won't it? Will that be on localhost using apache as a reverse proxy? Will everything still be packaged in one zip file as today?

[marc-vanderwal]

Dancer can spawn a small HTTP server for testing purposes, but when deploying a Dancer app in production, it can also spawn a FastCGI server, which is less expensive.

[hannaeko]

Danser will create daemon listening to http, won't it? Will that be on localhost using apache as a reverse proxy?

yes, there will be a reverse proxy in front either way

Will everything still be packaged in one zip file as today?

No it will be packaged as a perl module.

[hannaeko]

I am delaying that for next release, I think this PR needs more thoughts.