update __getitem__ to intercept specific prefixes

[jgostick]

If __getitem__ were upgraded it could intercept any dict keys that don't start with pore or throat, like 'parameter.temperature' and if found it could fetch the value from the parameters attribute of the object. This would allow automatically having all pore scale models look up values from different places other than the object's own dict. The parameters look-up could also work like the interleave data method, buy looking on self first, then parent object, then project if necessary.

This is a bit 'magic', but very handy and could be a good alternative to allowing new prefixes into the dictionaries, which will be a nightmare to change.

[jgostick]

The new Base refactor will be allowing 'param' in the dicts, so pore-scale models could work like this:

def viscosity(target, temperature='pore.temperature'):
	mu = f(temperature)
	return mu

Note that 'pore.temperature' is the default value, but the user could call it like:

viscosity(target=geo, temperature='param.T')

Thanks to Numpy's vectorization this can be done with 0 effort/changes inside the functions.