Core display options

[robertsj]

Currently, the core display is defaulted to burnup. It would be good to allow colors based on

• burnup
• enrichment
• power (possibly with the hottest bundle in a special color)
  and possibly others.

[nhorelik]

I made a branch of your repo and made these changes, as well as deleted
some unused files. For power peaking it reads from the Assembly.peak
attribute, so we'll need the reactor to make sure to update those values
after each evaluation for the coredisplay widget to pick them up.

[robertsj]

Cool. Is it possible to merge your edits with master? (I'm sure there's a good "best practice" cheat sheet for doing it.) I'll add the reactor peaking update during my next edit.

[nhorelik]

I went ahead and merged the branch with the changes to the master.