Provide survey setup functions

[ar4]

A somewhat tedious part of using Deepwave is the need to construct Tensors containing the source and receiver locations. It would be more convenient for users if there were functions that created these for common layouts when a few parameters are specified. For example, it could be capable of producing the location Tensors for a simple towed geometry when given the source and receiver spacing, the number of shots and receivers per shot, the distance from the closest receiver to the source, and the initial source location.

There is currently a Ricker wavelet function in the test directory, which is used during the automated tests, but this should probably be brought out into the main package so that users can easily create source amplitude Tensors with typical source wavelets.