View Transform improvements

Clamping is now done directly in the zoomBy/moveBy modifiers instead
of a separate clamping method. This allows returning the effective
factor/offset, which is used in the zoomBy:withCenter method to keep
the mouse cursor pointed at the same thing. The modifiers are now
more clear in which coordinate system they expect their arguments to be.
View Modifier: moveToLayer:newPos

An other new modifier that moves to a layer position. It is now used
by the relative modifier moveByLayer:offset and indirectly by the
all others.
Shift Layout

The "Shift Layout" functionality can change the even/odd page assignment.
It changes the current page from left to right side or vice versa, and
changes all other pages to match. This has no effect if the current page
is a double page. This does not change the layout order from left-to-right
or vice versa.