Add interactive plots with Plotly

[javierbg]

Description

This pull request adds a new module to the dashboard for showing interactive plots in the browser.

Motivation and Context

See issue #162

Checklist:

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

[javierbg]

Do you consider that a new test is needed for the module?

[codecov[bot]]

Codecov Report

Merging #163 (24a9aa2) into master (21c3cb7) will decrease coverage by 0.19%. The diff coverage is 70.58%.

:exclamation: Current head 24a9aa2 differs from pull request most recent head 121578f. Consider uploading reports for the commit 121578f to get more accurate results

@@            Coverage Diff             @@
##           master     #163      +/-   ##
==========================================
- Coverage   73.83%   73.64%   -0.20%     
==========================================
  Files          20       21       +1     
  Lines         795      846      +51     
==========================================
+ Hits          587      623      +36     
- Misses        208      223      +15     

Impacted Files	Coverage Δ
signac_dashboard/modules/plotly_viewer.py	70.00% <70.00%> (ø)
signac_dashboard/modules/__init__.py	100.00% <100.00%> (ø)

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[bdice]

Do you consider that a new test is needed for the module?

Explicit tests aren't needed -- the testing framework is pretty weak right now, and this should be automatically covered by the "kitchen sink" tests. However, an example would be good to include.

[Charlottez112]

I agree with Bradley. This seems very useful. Thank you for the implementation! If you could include an example, I'll also test it locally on my machine.

[javierbg]

I'm not familiarized with Flask, so when it came to add the routes and assets I just used other modules as reference (I think it was the DocumentEditor module).

When adding the Plotly CDN URL I realized that the "filename" attribute in line 104 was not used, apparently, so I removed it. Is this ok?