Fixes #464 Add Image search support of Yahoo

[bhaveshAn]

Fixes #464
Addresses #321

Checklist

• I have read the Contribution & Best practices Guide and my PR follows them.
• My branch is up-to-date with the Upstream master branch.
• I have added necessary documentation (if appropriate)

Changes proposed in this pull request:

• Added Image search support of Yahoo

Providing heroku deployment at https://mysterious-forest-53910.herokuapp.com/
@mariobehling @vaibhavsingh97 @ParthS007 Please review. Thanks !!

[Remorax]

I already made a PR 3-4 days back @bhaveshAn. Can this be closed? Thanks 😄

[bhaveshAn]

then just reference the issue 464 in your PR in title and PR desc

[codecov]

Codecov Report

Merging #465 into master will decrease coverage by 1.87%.
The diff coverage is 28.57%.

@@            Coverage Diff             @@
##           master     #465      +/-   ##
==========================================
- Coverage   89.15%   87.28%   -1.88%     
==========================================
  Files          28       28              
  Lines         664      684      +20     
==========================================
+ Hits          592      597       +5     
- Misses         72       87      +15

Impacted Files	Coverage Δ
app/server.py	84.88% <100%> (+0.17%)	⬆️
app/scrapers/generalized.py	75% <11.11%> (-11.28%)	⬇️
app/scrapers/yahoo.py	65.9% <25%> (-9.1%)	⬇️
app/scrapers/__init__.py	92.3% <50%> (-3.53%)	⬇️

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