selectAll is missing in SpAbstractTreePresenter

[hernanmd]

Just noticed there is a unselectAll method but no selectAll which could be very handy for lists where items are not using a checkbox.

[estebanlm]

thing is, there is no logical interpretation of what "selectAll" would mean in the context of a tree.

• expand all and select any element?
• select all the sibling nodes of current selection?
• select all the hierarchy and siblings of current selection?

hence, selectAll was never implemented, letting the user to cover that behavior (a bit more cumbersome, but more appropriate IMO).