discover CSX files as launch targets

[filipw]

This PR enables CSX to be discovered as valid OmniSharp launch points.
Allows CSX intellisense / language services to be used without a "fake" project.json that's currently needed (for OmniSharp to light up).

[DustinCampbell]

Is this the right experience? Should OmniSharp be launched on a particular .csx? Or should all csx files just be loaded by default?

[filipw]

good point, OmniSharp will just load all the CSX files starting from the entry directory, so we don't need to launch OmniSharp at a specific CSX file.
So maybe the best idea is to always include a root-level single "catch-all" CSX launch target?

I still think a CSX launch target (even if it's a root catch all one) needs to be there for OmniSharp to light up at all; in many cases (i.e. CSX files under folders containing sln/csproj/project.json) it wouldn't be needed at all, but in case where those are not there at all (i.e. folder is CSX only or CSX is outside of the slns/csproj/project.json) it's required

[filipw]

I pushed this change, let me know if it makes more sense now

[DustinCampbell]

Sorry for the delay @filipw. I think this is fine for now. I want to revisit the whole launcher logic since it's pretty clunky. However, your change seems good with the current state of the world. 😄