Filter option for OTF videos that will 404

[hbmartin]

• Adds is_otf property to Stream
• Filter like like for s in yt.streams.otf().all(): ... to avoid 404s
• Also, adds a filesize_approx stream property accurate to <0.1MB to avoid HTTP calls
• Refactors player config extraction (works better with age protected videos)
• Don't do unnecessary embed_html loading
• Ignore sts if unavailable when loading age protected videos
• Cleans up unnecessary functions in extract
• Adds flake8 linting plugins

[coveralls]

Coverage increased (+0.02%) to 91.788% when pulling 8f9dd791ae5e2ca63254e2df2412710409d44701 on error-404 into ea14b7b1c04e585a5836737eb0d1483cff75466a on master.

[codecov[bot]]

Codecov Report

Merging #48 into master will increase coverage by 0.02%. The diff coverage is 80.95%.

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
+ Coverage   91.64%   91.67%   +0.02%     
==========================================
  Files          14       14              
  Lines         922      949      +27     
==========================================
+ Hits          845      870      +25     
- Misses         77       79       +2

Impacted Files	Coverage Δ
pytube/monostate.py	86.66% <100%> (+2.05%)	:arrow_up:
pytube/query.py	100% <100%> (ø)	:arrow_up:
pytube/streams.py	93.49% <100%> (+0.45%)	:arrow_up:
pytube/__main__.py	82.22% <42.1%> (-2.82%)	:arrow_down:
pytube/extract.py	93.75% <96.15%> (+3.09%)	:arrow_up:

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[hbmartin]

@swiftyy-mage @movraxrsp I know y'all have looked into these issues before and I'm a bit nervous since taken together these are real changes to decrypting the streams. Can you take a look and try out with a few different videos?

[swiftyy-mage]

@hbmartin Will do.

[hbmartin]

@jslay88 can you try this branch and verify that it addresses #47 ? After that I can cut a release with these changes.