Ensure function names are at the top of files

[bencox]

ISSUE: In +kwave/+toolbox/@AcousticSolver/autoComputeTimeStep.m the first line should be
%% autoComputeTimeStep
but it is currently
%% autoCompute Time Step.
Similarly with other files, eg. executeTimeStep.m wrongly has %% execute Time Step instead of %% executeTimeStep, and gradient.m has %% The Gradient instead of %% gradient.

FIX: Update the first line of each file so that it corresponds to the filename (and also the function name).