Updated remote modal

[cabidop]

This is a revamp of the remote modal to include the following changes:

• Removal of the deprecation warnings according to this guide (similar approach as with the "import page" modal in Fixed deprecation warnings and bugs on page operations #11)
• Simplification of the component flow by using the buffered-content Discourse mixin instead of a custom implementation.
• Addition of a reset button to remove the remote configuration if it exists (only EmberJS code as the Rails endpoint was already present).

[angusmcleod]

@cabidop Looks good! The only (minor) thing I'm noticing is that the addition of the reset button means that the modal footer is not quite wide enough to accommodate the loading spinner without expanding slightly when it appears. The width of the modal shouldn't change.

https://www.loom.com/share/7f437bdd20214cb29d1ba280b10015f0

[cabidop]

Fixed, @angusmcleod, after the modal upgrade the CSS classes were not being properly picked and there was no min-width being set for the container.

[angusmcleod]

@cabidop I'm being pedantic I know, but the cancel button is moving now :)

https://www.loom.com/share/16274d86c37d43e29f3c598e3a6b67fb

Perhaps we can align that on the right of the footer? Just visually it doesn't look great when other elements are moved by a loading spinner. Sorry to be so picky. You seem on top of things though, so I think you can handle being held to a high standard.

[cabidop]

No worries, @angusmcleod! It was actually another "broken" style from the modal upgrade so the cancel button should be properly aligned now.

[angusmcleod]

@cabidop Looks good 👍