[MRG] Clean up net.cell_response

[ntolley]

#644 has brought to light a few bugs with how the CellResponse object is instantiated. Mainly trying to clean up the logic here.

Also removing the cell response indexing that nobody used or knows exists :wink:

[ntolley]

@jasmainak I've removed the __get_item__() functionality as I think it added a lot of complexity that was until now, mostly untested and documented.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 92.53%. Comparing base (819f4f4) to head (ba2616c). Report is 58 commits behind head on master.

:exclamation: Current head ba2616c differs from pull request most recent head f20ad9b

Please upload reports for the commit f20ad9b to get more accurate results.

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #647      +/-   ##
==========================================
+ Coverage   92.33%   92.53%   +0.20%     
==========================================
  Files          27       22       -5     
  Lines        5059     4343     -716     
==========================================
- Hits         4671     4019     -652     
+ Misses        388      324      -64     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[ntolley]

@rythorpe @jasmainak @katduecker this is ready to go! The main goal was to remove the overly complicated cell_response indexing functionality

[jasmainak]

looks good @ntolley

can you update whats_new.rst?

[ntolley]

@gtdang this is a pretty small PR that was supposed to be merged but was forgotten when things were stalled with the unit tests failing

It'd be good to have this merged before we make the release, it's main purpose is to remove an unused feature in the CellResponse class