Working with Block Actions from the keyboard

[neSpecc]

• When Tab is pressed in non-empty block, open Block Tunes Pane and set focus on the first active element
• Create blockTunesButtons getter that would find available elements by api.styles.settingsButton selector and [clickable] attribute for those, who want to use own classes. Also, find editable elements with utils/dom/canSetCaret method. It should find element both at the tool settings zone and at the default settings zone.
• When Block Tunes are opened, by Tab leaf focused button
• When one of Block Tunes buttons is focused, by Enter fire click on this tune if it is button, or set caret if it is an editable element (input).
• When Block Tunes are opened, by Escape close Block tunes and highlight current block to allow to continue working with keyboard.