Support netcdf

[sgrieve]

Investigate if this is possible within the scope of the hackday.

[sammiebuzzard]

Possible given more time:
-May not contain the same information as DEM files (e.g. projection often not given explicitly)
-Less useful in this case than from DEMs as if done properly the nc header will give enough useful information for reproducibility... but for consistency would be nice to have the ability to add this info e.g. to help make this a standard for submission of datasets with paper.