Volumetric Spin Prior in lalinference o2

Patch to add volumetric spin prior to lalinference_o2. Simple implementation of patch to Master by John Veitch:

https://bugs.ligo.org/redmine/issues/5020

Test of build & volumetric spin prior option here:

https://ldas-jobs.ligo.caltech.edu/~geraint.pratten/O2/G296853/C02/Production/PriorsStudy/C02_HLV_Clean_Priors_v3Priors_VolSpinPr/lalinferencenest/IMRPhenomPv2pseudoFourPN/1186302519.75-0/V1H1L1/posplots.html

compared to default priors:

https://ldas-jobs.ligo.caltech.edu/~geraint.pratten/O2/G296853/C02/Production/PriorsStudy/C02_HLV_Clean_Priors_v3Priors/lalinferencenest/IMRPhenomPv2pseudoFourPN/1186302519.75-0/V1H1L1/posplots.html