[Settings] Saving and retrieving

- Adding `ng-model` directive to editor element to bind the value that gets applied via `setValue()` of the editor to the `html` property in `settings.additionalParams`
- Controller updated to revise some variable names, add `html` as a prop to `additionalParams` object and $watch the `html` value and check for the scenario that no previous html saved so the default HTML can get applied
- e2e tests updated to run a test for saving settings