The standard DIM() macro was not typesafe as it happily deferred errors
to runtime that can be caught at compile time. Replacing it with a
generic C++11 constexpr allows for typecasting, comparison and compile
time error checking.
Primary change is to replace most control/window borders with
AUI pane borders. We implement our own AUI border drawing
routine which avoids the ugly one-pixel white frames around
dark canvasses.
Also increases the signal-to-noise ratio of all the pane
creation code in the various frames.