Add `RampFilter`

[garrettwrong]

Currently we have a few places in the code making use of a 2d ramp or 2d bump functions. We received feedback that it might be more useful to expose this as a Filter. Completing this issue consists of creating required Filter(s), replacing them in relevant areas of code, and incorporating them into an existing/new tutorial.

[janden]

So these would correspond to some sort of highpass and lowpass filters (i.e., multiplying by ramp or bump in the Fourier domain, respectively)?

[garrettwrong]

Yes. Perhaps "more useful" was poor wording on my part.

[janden]

No that's fine. Just making sure I understood what was meant here. If we have uses for these filters, I don't see why we shouldn't add them.