Invalid UI state when pressing undo after uploading an image

[noisysocks]

Describe the bug
It's possible to put the image block into a weird UI state by pressing undo after you upload an image using drag-and-drop.

To Reproduce

1. Insert an image block
2. Drag an image file onto the placeholder to upload it
3. Wait until the media has finished uploading
4. Press Undo

Expected behavior
The placeholder should be shown again. Instead, the image block pulsates as if it were still uploading.

Screenshots

Desktop (please complete the following information):

• OS: macOS 10.13.6
• Browser: Chrome 67.0.3396.99

Additional context
This also happens when the block is created by drag-and-dropping media directly into the editor. The Gallery and File blocks have similar bugs as well.

The problem is that we use the href attribute to store the blob: URL of the media that is being uploaded. This causes other related bugs, too. For example, if you refresh the page while media is uploading, the block doesn't display correctly.

We probably should be using this.setState() instead of this.props.setAttributes() to store intermittent data such as the file that is currently being uploaded. It's not clear how we would support file transforms if we do this, though.

[noisysocks]

Oops, this is a dupe of #3553.