Error on invalid config data

[vyasr]

Description

This PR changes the behavior of signac when an invalid log file is detected. Rather than just logging a debug-level error, it raises an exception.

Motivation and Context

An invalid config can lead to numerous other internal issues and is better to be raised loudly.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• The changes introduced by this pull request are covered by existing or newly introduced tests.
• The package documentation and framework documentation in signac-docs are up to date with these changes.
• I have updated the changelog and added any related issue and pull request numbers for future reference.

[codecov]

Codecov Report

Merging #855 (cb13068) into master (6390077) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #855   +/-   ##
=======================================
  Coverage   85.02%   85.02%           
=======================================
  Files          50       50           
  Lines        4668     4668           
  Branches      924      924           
=======================================
  Hits         3969     3969           
  Misses        519      519           
  Partials      180      180           

Impacted Files	Coverage Δ
signac/common/config.py	89.39% <0.00%> (ø)

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