Look into optimizing global #include's

[azonenberg]

We have a ton of stuff in scopehal.h and scopeprotocols.h that isn't truly needed project wide. Can we reduce the scope of some individual filter class headers etc so they're not being included project-wide and slowing down the build?

[tarunik]

Do we want this to be a one-time pass, or an ongoing header-patrol effort? Either way, include-what-you-use seems like the tool for this job...

[azonenberg]

For now, a one-time pass is probably adequate.