Fix assignment upload grading

[adityacp]

• Add a separate URL in code server to get file urls and download it in the student directory.
• Add a celery task to send all question files at once to the code server at the start of the quiz instead of sending the files during evaluation.
• Change assignment file urls instead of absolute path to the code server for evaluation.
• Fix issue while deleting the Lesson file.

[pep8speaks]

Hello @adityacp! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file api/views.py:

Line 209:80: E501 line too long (91 > 79 characters)

• In the file yaksh/file_utils.py:

Line 95:1: W391 blank line at end of file

Comment last updated at 2021-04-26 05:20:53 UTC

[codecov-commenter]

Codecov Report

Merging #833 (5ed0f0a) into master (4756f86) will decrease coverage by 0.38%.
The diff coverage is 43.63%.

@@            Coverage Diff             @@
##           master     #833      +/-   ##
==========================================
- Coverage   76.69%   76.30%   -0.39%     
==========================================
  Files          53       53              
  Lines        7684     7761      +77     
  Branches     1166     1177      +11     
==========================================
+ Hits         5893     5922      +29     
- Misses       1408     1453      +45     
- Partials      383      386       +3     

Impacted Files	Coverage Δ
yaksh/code_server.py	78.26% <25.00%> (-6.99%)	⬇️
yaksh/file_utils.py	64.38% <39.13%> (-12.09%)	⬇️
yaksh/models.py	85.08% <41.66%> (-0.10%)	⬇️
yaksh/tasks.py	72.85% <43.47%> (-5.78%)	⬇️
yaksh/hook_evaluator.py	74.00% <50.00%> (-4.85%)	⬇️
yaksh/views.py	70.67% <60.00%> (+0.07%)	⬆️
api/views.py	75.83% <100.00%> (-0.91%)	⬇️
yaksh/settings.py	100.00% <100.00%> (ø)

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