Added a check to Geometry that throws an error if the label already exists
Added tic and toc methods, to mimic the matlab timer
- pn.tic() resets it and pn.toc() stops it.
Updates to Import Network class
- It now works in the spirit of the other Networks
- Had to adjust the data setter to 'squeeze' (N,1) down to (N,).  This is a good general addition.
- Adjusted GenericGeometry, if neither pnums nor tnums are sent, then both get changed to 'all' so geometry applies everywhere, otherwise, if only pnums or tnums is sent, the other stays as [] which creates label but assigns it to no pores or throats.