Add support for new Spinnaker install location on MacOS, add reset!(cam), tweak framerate!(cam)

[IanButterworth]

A few changes:

1. FLIR changed the Spinnaker SDK install location in MacOS. This adds searching in that second location too. It also moves to a ref const library path so that julia doesn't need to rebuild the package if the library has moved. The cost of moving to a ref should be negligible

   
   julia> s = "hello"
   "hello"

julia> sr = Ref{String}("hello") Base.RefValue{String}("hello")

julia> @btime s * s 33.544 ns (1 allocation: 32 bytes) "hellohello"

julia> @btime sr[] * sr[] 54.121 ns (1 allocation: 32 bytes) "hellohello"

2. Adds `reset!(cam)` which immediately power cycles the camera

3. Only tries to set `AcquisitionFrameRateAuto` when setting the framerate, as some cameras don't support auto framerate

[samuelpowell]

Thanks @ianshmean, I have no means to test at the moment (and thus nothing to lose either). I've eyeballed the PR and it looks sane but it's up to you to confirm it works!

[IanButterworth]

Ok. I can confirm that it's working for me. I'll merge and release.