Flattened Gaussian Transverse before and after focusing

[rob-shalloo]

The flattened Gaussian transverse profile #349 adds a much needed profile to lasy, however, this profile only defines after focusing (ie. near the focus).

For a variety of use cases, it would make sense to have access to both the near field (ie before focusing with an OAP) and far field (i.e near focus) profiles.

I think we should add the near field profile too, either via an option in the profile or via the creation of a second profile.