Make the flow of using templates better

For users who:
- want to send messages from a template
- want to edit templates

For developers:
- who need to get the ID of a template

This commit mainly cleans up the choose template page so there are less
options, and the options that are there are less wordy.

This means:
- moving ‘send yourself a test’ onto the send messages page, and making
  it button
- stripping a lot of stuff out of the ‘send from API’ page, so it’s more
  obvious what the template ID is

tests/app/main/views/test_send.py

@@ -419,10 +419,6 @@ def test_route_choose_template_send_messages_permissions(mocker,
             "main.send_messages",
             service_id=service_one['id'],
             template_id=template_id) in page
-        assert url_for(
-            "main.send_message_to_self",
-            service_id=service_one['id'],
-            template_id=template_id) in page
         assert url_for(
             "main.edit_service_template",
             service_id=service_one['id'],