Factor resource management into dedicated functions

Create RFLResource namespace with functions to initialize
resource location (via binreloc) plus functions to return
application directory and locate and return path to an internal
resource.

Only implement as Mac App Bundle for now because of simple and
isolated layout. POSIX style layout should also work, but relative
path needs configuration.

Paths are canonized and checked with boost::filesystem, though just
as an implementation detail.
Set resource locations for Mac

Update resource configuration to use MACOSX_PACKAGE_LOCATION rather
than RESOURCE. The latter seems to only work consistently for
frameworks rather than bundles.

No guarantee of correct Linux functionality.