Add multiple ‘edit’ links for letter templates

Letter templates have (or will have) multiple different editable
regions. I think that the most intuitive way for this to work is to have
- an edit link for each of these areas
- positioned next to the thing to be edited

Again, this isn’t fully hooked up, but since no-one is using letters
live yet this is a good way of getting research feedback and pointing
towards where we want the feature to go.

Uses percentages for the positioning so that the alignment is maintained
on mobile.

app/main/forms.py

@@ -288,7 +288,18 @@ class EmailTemplateForm(BaseTemplateForm):
 
 
 class LetterTemplateForm(EmailTemplateForm):
-    pass
+
+    subject = TextAreaField(
+        u'Title',
+        validators=[DataRequired(message="Can’t be empty")])
+
+    template_content = TextAreaField(
+        u'Body',
+        validators=[
+            DataRequired(message="Can’t be empty"),
+            NoCommasInPlaceHolders()
+        ]
+    )
 
 
 class ForgotPasswordForm(Form):