Implement jet area calculations

[mattleblanc]

The area of a jet has several applications when associating different objects using ghosts, and when performing calibrations, particularly for subtraction of the average contribution from pile-up to a jet:

https://arxiv.org/abs/2007.02645

https://arxiv.org/pdf/1107.4277

The methods used to calculate the jet are are documented by Cacciari et al., and available in fastjet:

https://arxiv.org/abs/0802.1188

https://github.com/alisw/fastjet/blob/a7a459d280f151197bc24676a243d9cafa065b81/fastjet/include/fastjet/ClusterSequenceAreaBase.hh

etc.

[mattleblanc]

If #123 goes well, our current plan is for @emadmtr to look at this afterwards.