new test macro in the latest macro format
test selection files
Update saved macro/filter/selection file extensions

To match the PD in PhotoDemon
Update common dialogs to match new macro/filter extensions

...while still providing access to the old formats
Provide a new /Selection subdirectory for saved selections

Saved inside the user directory, and updated if/when the user selects a
new directory
User-facing load/save selection menus

WARNING: STILL BUGGY!  This commit is primarily archival.  I need to do
an epic refactoring of the core selection code before I can successfully
debug a number of selection-related functions.

Right now, the pdSelection class contains a horrible mishmash of
presentation and domain code, and until I separate out the interface
stuff, I can't successfully debug all the latest selection
implementations.  Work on refactoring is underway, but I wanted to sync
this commit before I start tearing everything apart.

WITH THAT IN MIND - if you are reading this commit, note that all things
selection-related will be in a heavy state of flux for the next few
weeks.  Please do not code against them until I've cleaned up the core
pdSelection class.