Add lazy load for images

[gautamjajoo]

This PR adds lazy loading on images and the images of the challenges are now loaded when the viewport changes, hence as the user moves down the logos are displayed.
@Ram81 @Kajol-Kumari

lazyimage.mp4

[codecov-commenter]

Codecov Report

Merging #3571 (b0b7fc2) into master (96968d6) will decrease coverage by 1.45%.
The diff coverage is 32.43%.

@@            Coverage Diff             @@
##           master    #3571      +/-   ##
==========================================
- Coverage   72.93%   71.47%   -1.46%     
==========================================
  Files          83       20      -63     
  Lines        5368     3232    -2136     
==========================================
- Hits         3915     2310    -1605     
+ Misses       1453      922     -531     

Impacted Files	Coverage Δ
frontend/src/js/controllers/authCtrl.js	53.91% <6.38%> (-12.95%)	⬇️
frontend/src/js/controllers/profileCtrl.js	79.76% <20.00%> (-13.10%)	⬇️
frontend/src/js/controllers/permissionCtrl.js	36.36% <22.22%> (-63.64%)	⬇️
frontend/src/js/controllers/challengeCtrl.js	63.41% <30.64%> (-10.29%)	⬇️
frontend/src/js/controllers/updateProfileCtrl.js	82.55% <44.44%> (-10.30%)	⬇️
frontend/src/js/controllers/challengeListCtrl.js	95.74% <50.00%> (+1.06%)	⬆️
...ntend/src/js/controllers/challengeHostTeamsCtrl.js	70.50% <66.66%> (-1.18%)	⬇️
frontend/src/js/controllers/teamsCtrl.js	71.17% <75.00%> (ø)
frontend/src/js/controllers/ChallengeInviteCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/SubmissionFilesCtrl.js	95.45% <100.00%> (ø)
... and 30 more

Impacted Files	Coverage Δ
frontend/src/js/controllers/authCtrl.js	53.91% <6.38%> (-12.95%)	⬇️
frontend/src/js/controllers/profileCtrl.js	79.76% <20.00%> (-13.10%)	⬇️
frontend/src/js/controllers/permissionCtrl.js	36.36% <22.22%> (-63.64%)	⬇️
frontend/src/js/controllers/challengeCtrl.js	63.41% <30.64%> (-10.29%)	⬇️
frontend/src/js/controllers/updateProfileCtrl.js	82.55% <44.44%> (-10.30%)	⬇️
frontend/src/js/controllers/challengeListCtrl.js	95.74% <50.00%> (+1.06%)	⬆️
...ntend/src/js/controllers/challengeHostTeamsCtrl.js	70.50% <66.66%> (-1.18%)	⬇️
frontend/src/js/controllers/teamsCtrl.js	71.17% <75.00%> (ø)
frontend/src/js/controllers/ChallengeInviteCtrl.js	100.00% <100.00%> (ø)
frontend/src/js/controllers/SubmissionFilesCtrl.js	95.45% <100.00%> (ø)
... and 30 more

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[gautamjajoo]

@Ram81 We can add this to all the images, but do we need to do that?

[Ram81]

LGTM. Tested locally, works fine