Introduce massaction mode for image delete

[sivaschenko]

Story #461

The context/mode property should be introduced to the media gallery components with two options: 'regular' and 'massaction'.
The default mode is 'regular'.
When 'massaction' mode is enabled (at this stage for the prototype - programmatically):

• The selected action buttons should be hidden
• The "three dots" context menu for the image should be hidden
• The ability to select multiple images should be enabled
• Number of selected records should be displayed in the breadcrumbs
• The slide panel title should be changed

AC

• User is able to switch tp massaction mode
• It is possible to select multiple images in the massaction mode
• Number of selected records to massaction mode is indicated
• Only Delete and Cancel buttons are shown in massaction mode
• Image context menu is removed in the massaction mode
• Selection checkboxes are added in massaction mode
• Covered with MFTF tests

[m2-assistant]

Hi @sivaschenko. Thank you for your report.
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