Adding more estimation fields to sprint poker

[acressall]

A user request:

sync more fields for the estimate time. Just to be precise, in my team we have front-end developers and back-end developers so in Jira we have a global estimation and a more precise estimation for front and back. It could be really better to have 2 fields in Parabol for the estimation, one for back-end and one for front-end.

I'm not sure how common this practice is, but now it's here so we can note if it comes up more!