Feature request: Have zero wave test

[dtgaebe]

Feature description.
We should include a test function that quickly let's a wec be simulated (not optimized) in order to check if there is drift etc...

[rgcoe]

so we would, e.g., allow you to call wec.solve(waves=None,...) and it would quickly generate a zero amplitude wave with the zero freq. at the fundamental of your frequency array?

[dtgaebe]

something like that! And if waves=None also no objective function is required.

[dtgaebe]

#325 is related