With multiple editor instances on page make sure opening a dialog sets the current toolbar's editor to the active one

[indigoxela]

It is possible to click into an editor (that one's the "active" one then), but then opening a dialog via another editor's toolbar.
That leads to content inserted in the "wrong" editor (and the progress state to be wrong, too).

Tiny's own dialogs set the focus on the editor, in which the toolbar button was clicked, and that seems reasonable, too, for our ajax dialogs.