Raise restriction on shared memory in container.

[mdales]

64MB, which is the default, is too small to be useful in a geospatial context. This changes it to 64GB, which might still be too small, but is a start, and lets me do some LIFE calculations that I couldn't before.

[mdales]

@patricoferris not sure why all the builds failed, but the couple I looked at it seems to be unrelated to the change.

[patricoferris]

Do you reckon we're going to want to make this configurable. Happy to make this the default if not supplied, just thinking ahead to any mega parallelism things that might get run ?

[mdales]

Well, I just hit a use case where 64GB isn't enough :/

We could configure it, but don't imagine most ecologists doing that. Is there a reason not to just make it significant proportion of physical memory? I can understand in the general docker case not doing that, but in this context I can't see why we'd impose any limits.