Address nan issue by trimming sweeps

[tmchartrand]

Overview:

One of two options to address issue #508 by trimming missing values from the end of sweeps as they are loaded. The other solution is probably my preferred one, but I'm open to either.

Type of Fix:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing
  functionality to not work as expected)
• Documentation Change

Solution:

Dropping nans from sweeps as they are loaded allows stim/epoch detection code to run without errors caused by nans.

Changes:

• follows the pattern previously used for trailing zeros, trimming nans as data is loaded.
• reduces the logging of sweep integrity tags from warning to info, as truncated sweeps are now common and expected.
• removes the "recording" epoch, which is now unnecessary (this could possibly break some user code and should be maybe replaced by deprecation warnings, but that seems unlikely)
• improved plot_data_set for quick visualization of new NWB2 to assess epochs

Validation:

Checked that tests pass and that epochs are found correctly without error in a new MIES NWB2 file using the updated plot_data_set

from ipfx.bin.plot_ephys_nwb import plot_data_set
from ipfx.dataset.create import create_ephys_data_set
path = '/allen/programs/celltypes/production/humancelltypes/prod148/Ephys_Roi_Result_1077533543/H21.26.402.12.58.01.05.nwb'
data_set = create_ephys_data_set(path)
plot_data_set(data_set, clamp_mode='CurrentClamp', show_amps=True, qc_sweeps=True)

Checklist

• My code follows
  Allen Institute Contribution Guidelines
• My code is unit tested and does not decrease test coverage
• I have performed a self review of my own code
• My code is well-documented, and the docstrings conform to
  Numpy Standards
• I have updated the documentation of the repository where
  appropriate
• The header on my commit includes the issue number
• My code passes all tests
• I have updated the CHANGELOG.md with the description of changes understandable by end users

[MatthewAitken]

Closing since issue is resolved by PR 520