Use keyword method instead of mode

[jgostick]

I have noticed that some numpy/scipy functions have (started) using this. I think I like it and it's slightly more descriptive. Is it worth making the change?

[jgostick]

'mode' would be used when a different result is returned, while 'method' would be a different way to compute the same result. Example would be method='tessellation' vs method='distance_matrix'.

[jgostick]

We should do a "find all" for the mode' in the function definitions, then create a list of all functions where this change might make sense here. Most function will probably remain with mode.

[jgostick]

For example, find_trapped_regions currently uses cluster labeling, which works fine/fast for pressure based drainage but for invasion percolation it is too slow, so we have created find_trapped_regions2. This should be accessible via find_trapped_regions by switching the method.