improve ophys docstrings

[bendichter]

Copy/paste description from the doc of the schema element where appropriate for better documentation

Motivation

I found in several cases that the doc in the schema is more informative than the docstrings in the functions. Since users are more likely to see these docstrings in the pynwb API documentation page than the doc in the schema yaml files, I decided to replace them where appropriate.

Also, it is best practice for one-liner docstrings to put the triple quotes on the same line as the text.

[codecov]

Codecov Report

Merging #1126 into dev will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff          @@
##             dev   #1126   +/-   ##
=====================================
  Coverage   67.5%   67.5%           
=====================================
  Files         38      38           
  Lines       2302    2302           
  Branches     397     397           
=====================================
  Hits        1554    1554           
  Misses       679     679           
  Partials      69      69

Impacted Files	Coverage Δ
src/pynwb/ophys.py	92.8% <ø> (ø)	⬆️

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