Implement mechanism in wx Gambit application object to locate external tools #79
Description
External solver tools are located in an ad-hoc way in dlnash, dlefglogit, and dlnfglogit. On Mac wxStandardPaths is used to locate these in the application bundle. On other platforms, it is simply assumed the tools are in ${PATH} or equivalent.
As a first step, this should be moved to a central facility in the Gambit wxApp instance. For the moment, wxStandardPaths (or similar) should be used across all platforms. At a later step, wxConfig could be used to implement custom pointers to tools.