Directory handling broken on Windows and Linux

[wibblemonkey]

I'm mainly using the SpectrumAnalyser on Windows and occasionally Ubuntu, and I'm struggling on both. I've noticed that whenever I try to run the application from the command line on Windows, it ignores the GlobalConfig.json in the application directory and creates one in the current working directory - it also creates an imgui.ini file.
Digging into the source, it seems that on the Mac, there's initialisation code that sets up values for Bundle, App Support and Documents directories, but there's nothing similar implemented for Windows or Linux - the corresponding calls just return the supplied filename, so the current working directory when the application is started is used.
I assume that the Bundle and App Support directories are Mac concepts and should both map to the application installation directory on Windows and Linux, and Documents should map to the user's Documents folder on both?

[wibblemonkey]

I believe this is also the root cause of issue #24 .