Pull ROTT data from various common install paths

[erysdren]

Heavily work in progress. It builds under Mingw, but it doesn't do any (much needed) Windows Registry checks for things such as the Steam directory and maybe others. For both Linux and Windows, it just queries the default installation paths from the various storefronts for each platform. It works, but it's not super elegant or foolproof. This does not conflict with the XDG paths or any others.

This also needs to be modified to account for where the game could be installed with GOG under Mac OS X.

[erysdren]

This actually causes a segfault in the COMM-BAT menu because it tries to display the filename of the RTC mapset. It uses the full filepath in a buffer of 80 chars which is not long enough for most of these.

[fabiangreffrath]

Heavily work in progress. It builds under Mingw, but it doesn't do any (much needed) Windows Registry checks for things such as the Steam directory and maybe others.

Do you plan to add that later?

[erysdren]

I do. I will likely import the appropriate code from Ironwail with the appropriate attribution, if possible.

[erysdren]

@fabiangreffrath Does this need any more work before merging?

[fabiangreffrath]

Not if you want to postpone the windows registry checks.

[erysdren]

I will add those as a separate PR later. Thank you!