Moves titles into templates and adds i18n support

bookwyrm/templates/discover/landing_layout.html

@@ -1,8 +1,10 @@
 {% extends 'layout.html' %}
 {% load i18n %}
 {% load bookwyrm_tags %}
-{% block content %}
 
+{% block title %}{% trans "Welcome" %}{% endblock %}
+
+{% block content %}
 <header class="block has-text-centered">
     <h1 class="title">{{ site.name }}</h1>
     <h2 class="subtitle">{{ site.instance_tagline }}</h2>