[FIX] Finish merging selcomps v2.5

[tsalo]

I think selcomps should work after these changes are merged.

Changes proposed in this pull request:

• Corrects getelbow import to getelbow_mod
• Add arguments mmix, manacc, and n_echos to selcomps.
  • We use mmix to get the number of volumes, which was originally used and stored as nt
  • This supports manually defined accepted components with manacc
  • n_echos was required (stored as ne) but wasn't defined
• Extract relevant fields from seldict rather than unpacking with eval
• This PR also includes recent commits to master

[emdupre]

❤️ thank you !!