Add prompt to add first template to dashboard

https://www.pivotaltracker.com/story/show/112814667

> As you need to have templates to send any notifications, we should be nudging
> people to do that when they sign in.
>
> This should be in the dashboard, with a link to manage templates.
>
> Should be bright and shiny and only show if the service has no templates.

This commit adds the above.

It also rationalises the language (some places used ‘create template’, others
used ‘add template’, this changes everything to the latter).

app/main/views/dashboard.py

@@ -2,6 +2,7 @@ from flask import (abort, render_template, session)
 from flask_login import login_required
 from app.main import main
 from app.main.dao.services_dao import get_service_by_id
+from app.main.dao import templates_dao
 from client.errors import HTTPError
 from ._jobs import jobs
 
@@ -9,6 +10,13 @@ from ._jobs import jobs
 @main.route("/services/<int:service_id>/dashboard")
 @login_required
 def service_dashboard(service_id):
+    try:
+        templates = templates_dao.get_service_templates(service_id)['data']
+    except HTTPError as e:
+        if e.status_code == 404:
+            abort(404)
+        else:
+            raise e
     try:
         service = get_service_by_id(service_id)
         session['service_name'] = service['data']['name']
@@ -22,4 +30,5 @@ def service_dashboard(service_id):
         jobs=jobs,
         free_text_messages_remaining='25,000',
         spent_this_month='0.00',
+        has_templates=bool(len(templates)),
         service_id=service_id)

app/templates/views/manage-templates.html

@@ -15,7 +15,7 @@ GOV.UK Notify | Manage templates
         <h1 class="heading-xlarge">Templates</h1>
 
         <p>
-          <a href="{{ url_for('.add_service_template', service_id=service_id) }}">Create new template</a>
+          <a href="{{ url_for('.add_service_template', service_id=service_id) }}">Add new template</a>
 
         {% for template in templates %}
           {% if template.get_field('template_type') == 'sms' %}

app/templates/views/service_dashboard.html

@@ -8,6 +8,15 @@
 
 {% block maincolumn_content %}
 
+    {% if not has_templates %}
+      {{ banner(
+        '<a href="{}">Add a template</a> to start sending notifications'.format(
+          url_for(".add_service_template", service_id=service_id)
+        )|safe,
+        type="tip"
+      )}}
+    {% endif %}
+
     <ul class="grid-row job-totals">
       <li class="column-half">
         {{ big_number(