Implementation of photoz uncertainties

[anicola]

This is an implementation of photoz uncertainties in the unbinned likelihood. It might still be a bit slow, but I thought I can optimize once we know how slow it is on the sample we will actually be using.

[itrharrison]

Thanks @anicola . I'm happy to just merge this seeing as it isn't going to the main branch yet. @eunseongleee I don't know if you just want to have a quick look to make sure nothing is going to break the dev-clusters-both branch? You may want to e.g. push anything you have to that branch then solve conflicts when merging this PR. Rather than merge this PR and end up with conflicts between the dev-clusters-both on here and any local changes you might have.

[eunseongleee]

Thanks a lot for the heads up @itrharrison and sorry that I'm checking this so late @anicola! I've pushed my latest version just now and hope things won't conflict! From a quick look, it doesn't look like it's gonna conflict, but please let me know if I need to do something about this.