* Add the option to use a logo for the top left site title

* Use | relLangURL for the base urlº

This way, when you click on the header it maintains you in the same language you previously selected.

* Use .Site.Home.RelPermalink as proposed by @regisphilibert

Reverts 0d9656d939 (diff-5c3a1b4da16de002912dd90a78641f32R12)

Fixes #229

Using the `{{ .URL }}` token results in a warning:

    WARN 2019/10/13 15:12:12 Page's .URL is deprecated and will be removed in a
    future release. Use .Permalink or .RelPermalink. If what you want is the
    front matter URL value, use .Params.url.

Steps to reproduce
==================

Follow along with the Quick Start guide at
https://gohugo.io/getting-started/quick-start/

Running `hugo server -D` emits a warning that `.URL` is deprecated.

* Create fr.toml

French translation

* Social link to "mastodon" added

* Some statics partials are cached, to optimise rendering

* Caching moved so that the i18n menu will work as expected. Refs #35