New AlphaBlend API support function for layers

Useful when rendering a layer directly to a DC with full alpha support.
Premultiplication is required, and layers do not currently offer a
premultiplication function, so the assumption is that the layer has been
directly created from an image in PD's resource section via GDI+ (so
premultiplied alpha is already in effect).
Non-functional formatting changes
New support function for loading PNG resources directly into pdLayer objects

Combined with ee33f60f71a36910a83d13bb9a08451983edf2c2, this provides a
very simple way to load 32bpp image resource and render it to any
interface element.
Improve messaging
Abandon dedicated Smart Resize tool; instead, merge features into current Resize tool

Changes are not yet implemented - I just wanted to push this commit so I
could get a number of other ones synched.

This commit also lays the framework for a Canvas Resize tool.