Use Gravatar SDK to download the image via URL

[pinarol]

Use Gravatar SDK to download the image via URL.

Changing the implementation of our new method

public func downloadGravatar(_ gravatar: GravatarURL?, placeholder: UIImage, animate: Bool, failure: ((Error?) -> ())? = nil) 

Test:

Impacted files in the WP repo:

• ListTableViewCell
• CommentContentTableViewCell
• NoteBlockCommentTableViewCell
• NoteBlockHeaderTableViewCell
• NoteBlockUserTableViewCell
• PeopleCell
• PersonViewController
• RevisionsTableViewCell
  NotificationContentView (I haven't figured how we can test this yet.)

Documentation of testing steps can be found here: wordpress-mobile/WordPress-iOS#22543 (comment) Please take a look and see if you can find anything odd. For now the avatars should be loading successfully.

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• I have considered if this change warrants release notes and have added them to the appropriate section in the CHANGELOG.md if necessary.

[etoledom]

Looking good!

Tested all paths in the same what than in wordpress-mobile/WordPress-iOS#22624 (review)

All smoke tests look good.

I did find something interesting which seem to come from the previous integration (not related to this PR).

In the notifications view, under low connectivity conditions, is visible when the reused cell has the previous image set, while the new image is loading:

I'm highlighting this as documentation, to let the WPiOS team know about this in case they would like to do something about it.

🎉