Add more feedback on disabling "Uniform Scaling" mode

Uniform Scaling mode means that your shape is not just "resized", but
"transformed" using a uniform transformation.

When you "resize" (uniform scaling disabled) a shape, you basically
change its local width and height (even when the shape is rotated
using some embedded transformation). Resizing can never shear or deform
your shape, that is a resized rectangle will always stay rectangular.

When you "uniform scale" a shape, you don't "resize" it, you apply a
transformation to it. That is all the small elements of the shape like
stroke, pattern and gradient will also become scaled. And if you apply
a uniform scale transform in global mode to a rotated shape, then
the shape will be scaled uniformly, and rectangle will become sheared.

NOTE1: Non-uniform scaling mode is available only when
       *one* shape is selected. "Resizing" multiple shapes
       in a non-uniform way is just not possible. Therefore the
       checkbox becomes automatically disabled when you select
       multiple shapes.

NOTE2: Groups do not support non-uniform "resizing" (see NOTE1).
       Technically, resizing of a group is just applying a common
       transformation on the top of the child shapes. Therefore, all
       the properties of the uniform scaling apply to this process.


CC:kimageshop@kde.org