Invert actions from editor bar

[vitonsky]

When user click "Insert header" and editor is focused on header, app will insert yet another header inside of header

Instead editor must invert operation.

• In case active object have the same formatting, it must be deleted. For example, user focus on element with H1 and click H1
• In case active object have different formatting, it must be changed to selected one. i.e. user focus on element with H1 and click H2