Reword the add service page

Without the preview service name we probably have to go back to communicating
a bit more on the add service page. This commit brings back the two bullet
points about where the service name will appear, and tries to tie it into the
nice words that Matt Sheret wrote for us.

app/main/forms.py

@@ -164,13 +164,13 @@ class AddServiceForm(Form):
     name = StringField(
         'Service name',
         validators=[
-            DataRequired(message='Service name can not be empty')
+            DataRequired(message='Service name can’t be empty')
         ]
     )
 
     def validate_name(self, a):
         if a.data in self._names_func():
-            raise ValidationError('Service name already exists')
+            raise ValidationError('This service name is already in use')
 
 
 class ServiceNameForm(Form):