Add toolbar to image block

[pinarol]

Description

This PR includes changes for adding toolbar to image block and also adding edit button in it.

How has this been tested?

• Refer to parent PR to find out how to setup the testing environment.

Test 1:

• Open a blog post
• Add image block, tap Media Library, select an image
• Add another image block but don't set an image for it
• Tap on the image block with an image set, verify that toolbar is visible
• Tap on the image block with no image is set, verify that toolbar isn't visible

Test 2:

• Open a blog post
• Add image block, tap Media Library, select an image
• See that toolbar appears with an edit button in it(pencil icon)
• Tap edit button in the toolbar
• Verify that image picker is opened, select an image
• Verify that image is changed in the image block

Test 3:

• Open a blog post
• Add image block, tap Media Library, select an image
• See that toolbar appears with an edit button in it(pencil icon)
• Tap edit button in the toolbar
• Verify that image picker is opened, tap "Cancel"
• Verify that image is NOT changed in the image block

Screenshots

Types of changes

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[pinarol]

Rafactored due to edit.js, ready to review again @etoledom @hypest

[hypest]

LGTM!