252 add envelope function to reliondataset

[DSilva27]

No description provided.

[mjo22]

After the "Particle Extraction" job in relion, the rlnCtfBfactor and rlnCtfScalefactor are unestimated and all set to 0 and 1, respectively. In a case like this, do we want to read in particle stacks with these fields or just set the envelope to None?

I guess an argument for always setting them is that we may not want behavior where depending on what exactly is in the STAR file, the fields change.

[DSilva27]

Setting the bfactor to 0 and the scale to 1 will just give you something equivalent to creating the transfer theory with the envelope set as None anyway. There is not really a reason to set it up that way, except maybe computational efficiency.

[mjo22]

Yeah, I suppose a user can always just setup a new transfer theory without the envelope if they want