Rewrite and Port Mapper Tool

[MadScienceZone]

The mapper client has badly needed some refactoring for a while, as well as being the only hold out from the version 3 GMA tool suite that's still written in Tcl/Tk. This issue is to port the tool away from a Tcl script and at the same time refactor all the code to be more sanely implemented and shake out the bugs that have crept in. The initial effort here is to port it to the Go language, in the hopes that the compiled binary will perform better and be simpler to install for end users. In addition to simply porting it, make the following upgrades while we're in there:

• Introduce file format 20, which changes from unorganized text lines marshaled as Tcl lists to a structured file with JSON marshaling.
  • The current version (17) file format must also be understood on input, although format 20 may be written unconditionally on output.
• Implement server protocol 400, which similarly changes the protocol from Tcl-list-based to JSON-based data marshaling.
• Change to OS-standard directories for storing cache and configuration files.

[MadScienceZone]

Work is already underway for version 4.0.0 of the mapper client which will include most of these changes. Probably everything except porting it to another language. Currently the rewrite is keeping the original Tcl code although much of that is changing internally as the object representation is different now as well as the external file and protocol formats. That is triggering a bit of needed refactoring, but eventually it would still be good to move it to a compiled language.