Move Gaussian drawing function from WSClean

CMakeLists.txt

include/schaapcommon/fitters/gaussianfitter.h

include/schaapcommon/math/compositefft.h

include/schaapcommon/math/convolution.h

include/schaapcommon/math/drawgaussian.h

include/schaapcommon/math/ellipse.h

include/schaapcommon/math/resampler.h

include/schaapcommon/math/restoreimage.h

src/fitters/gaussianfitter.cc

src/fitters/test/tgaussianfitter.cc

src/math/CMakeLists.txt

src/math/compositefft.cc

src/math/convolution.cc

src/math/drawgaussian.cc

src/math/resampler.cc

src/math/restoreimage.cc

src/math/test/CMakeLists.txt

src/math/test/runtests.cc

src/math/test/tconvolution.cc

src/math/test/tresampler.cc