Cannot disable external apps & saving settings for External Apps does not give confirm message

Related to this bug: https://bugs.launchpad.net/mahara/+bug/1947528

When updating the an external apps configuration settings, there are two issues:
1. There is no confirm message to say that the settings were updated
2. The enable switch remains on 'Yes' even when you switch it to 'No'

Steps to reproduce:
1. Go to Web services>External Apps
2. Type a new name in the 'Application' field.
3. Select LTI 1.1 from the dropdown
4. Click 'Add' (you will be taken to the edit screen)
5. Click 'Save'

Expected outcome:
 - Redirected to main external apps page, with a confirmation banner saying 'The configuration settings for x app have been saved.'

Actual outcome:
 - Edit page reloads with no confirmation message

Continued:
6. On the app's edit page, click the 'Enabled' switch to change it to 'No'
7. Click 'Save'

Expected outcome
 - Redirected to main external apps page, with a confirmation banner saying 'The configuration settings for x app have been saved.'
- When revisiting the edit page for this app, the 'Enabled' switch should be set to 'No'

Actual outcome
 - Edit page reloads with no confirmation message
 - 'Enabled' switch has changed back to 'Yes'

Will only need to check for apps registered with LTI, Moodle and LTI Advantage (Not mobile or other non-oauth apps: This has already been prevented in this patch here: https://reviews.mahara.org/12330)

It may also be worth checking with an external app that has been registered with a custom webservice group that uses an LTI function.