Add option for showing bookmark favicons (#390)

* Implement favicon loader

* Implement load favicon task

* Show favicons in bookmark list

* Add missing migration

* Load missing favicons on import

* Automatically refresh favicons

* Add enable favicon setting

* Update uwsgi config to host favicons

* Improve settings wording

* Fix favicon loader test setup

* Document LD_FAVICON_PROVIDER setting

* Add refresh favicons button

uwsgi.ini

@@ -1,8 +1,8 @@
 [uwsgi]
-chdir = /etc/linkding
 module = siteroot.wsgi:application
 env = DJANGO_SETTINGS_MODULE=siteroot.settings.prod
 static-map = /static=static
+static-map = /static=data/favicons
 processes = 2
 threads = 2
 pidfile = /tmp/linkding.pid
@@ -15,6 +15,7 @@ die-on-term = true
 
 if-env = LD_CONTEXT_PATH
 static-map = /%(_)static=static
+static-map = /%(_)static=data/favicons
 endif =
 
 if-env = LD_REQUEST_TIMEOUT