[Channel Manager] Make save always active

When a newly added component is edited, required field values will be missing. All required fields have to be set before the component can be saved. When a component has many parameters, it's hard to see which ones are required since fields only become red once touched.

Steps to reproduce:

1. In the HAP, add a new News List component
2. Edit the newly added News List
3. Try to save it

Expected: it's clear that there's one required field ("News Document types") that has to be filled in before changes can be saved.

Actual: the user is lost in a maze of fields and does not understand why the 'Save' button remains disabled.

See comment by cdekort: Now that we're replacing the CLOSE button with DISCARD we can use that button to indicate that changes have been made: DISCARD is disabled if there are no changes and enabled if there are**.
SAVE in the visual editor then can be enabled always. If fields are not filled correctly their error messages appear on SAVE and the first error field gets focus