[Refactor] Rename the app module to calsocial

Just for clarity

calsocial/templates/index.html

@@ -0,0 +1,9 @@
+{% extends 'base.html' %}
+
+{% block content %}
+{{ _('Welcome to Calendar.social, %(username)s!', username=current_user.username) }}
+
+{% include 'month-view.html' %}
+
+<a href="{{ url_for('new_event') }}">{% trans %}Add event{% endtrans %}</a>
+{% endblock content %}