[mod] Revision of the favicon solution

All favicons implementations have been documented and moved to the Python
package:

    searx.favicons

There is a configuration (based on Pydantic) for the favicons and all its
components:

    searx.favicons.config

A solution for caching favicons has been implemented:

    searx.favicon.cache

If the favicon is already in the cache, the returned URL is a data URL [1]
(something like `data:image/png;base64,...`).  By generating a data url from
the FaviconCache, additional HTTP roundtripps via the favicon_proxy are saved:

    favicons.proxy.favicon_url

The favicon proxy service now sets a HTTP header "Cache-Control: max-age=...":

    favicons.proxy.favicon_proxy

The resolvers now also provide the mime type (data, mime):

    searx.favicon.resolvers

[1] https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URLs

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/favicons/__main__.py

@@ -0,0 +1,12 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""Command line implementation"""
+
+import typer
+
+from . import cache
+from . import init
+
+init()
+app = typer.Typer()
+app.add_typer(cache.app, name="cache", help="commands related to the cache")
+app()