Revert "put all the buttons in a toolbar"

This reverts commit 245cbd402b3b0d07ce281851e6305594ece013a9.

Thing is, using a full-width toolbar just to make the buttons
appear after installation is an overkill. The toolbar will be mostly
empty and the user is very likely to move the buttons elsewhere and hide
it.

Instead of this pollution, the extension description shall include sort
instruction where to find the newly available buttons.

Notably, making the buttons appear right after installation is not
feasibly for several reasons:
 * detecting "right after installation" is not trivial
 * finding the right toolbar to add the buttons to is impossible, as
   "right" is user-dependent.