Purge static-typed variables

Additional testing and research showed no speed benefit for static
typing, and in fact a possible speed loss.

All static variables (that weren't explicitly required to be static) are
now declared using conventional Dim.
new Filter Support class, all Distort tools updated

The new class internally manages all custom edge handling and
interpolation.  This allows me to make central changes, which are then
distributed across all distort-style tools.

It was also the only easy way to add custom edge handling to all distort
tools.