Gallery view: image editing toolbar

[kirillt]

After #10 the user will be able to walk through the images.

There also must be a toolbar with image editing operations:

• Rotate
• Brush
• Blur
• Crop
• Text

Each of operations switches image mode from viewing to editing. Each operation has the same logic of cancelling the operation, i.e. leaving the editing mode without applying the operation. We could implement it in this scope:

• mark the editing mode when any operation is clicked
• remove editing marks when "cancel" button is clicked

Discuss with Sona:

• should we display "cancel" button when we activate any of the operations?
• should it be possible to hide the toolbar?