Add flake8, autopep8, and pycln to CI

[Archmonger]

This PR adds in PEP8 conformity throughout the repo.

New CI hooks

• flake8: Provides error messages for PEP8 violations
• autopep8: Automatically fixes most PEP8 violations
• pycln: Automatically fixes PEP8 unused imports violations

[codecov]

Codecov Report

Merging #512 (a241f06) into master (8a8ac08) will decrease coverage by 0.01%.
The diff coverage is 72.72%.

@@            Coverage Diff             @@
##           master     #512      +/-   ##
==========================================
- Coverage   84.61%   84.60%   -0.02%     
==========================================
  Files          51       51              
  Lines        2061     2059       -2     
==========================================
- Hits         1744     1742       -2     
  Misses        317      317              

Impacted Files	Coverage Δ
silk/model_factory.py	83.84% <0.00%> (ø)
silk/profiling/dynamic.py	83.47% <ø> (-0.15%)	⬇️
silk/templatetags/silk_inclusion.py	96.55% <ø> (ø)
silk/templatetags/silk_filters.py	66.17% <50.00%> (ø)
silk/sql.py	78.46% <75.00%> (ø)
silk/middleware.py	89.42% <100.00%> (+0.10%)	⬆️
silk/models.py	87.22% <100.00%> (-0.06%)	⬇️
silk/views/cprofile.py	69.23% <100.00%> (-2.20%)	⬇️

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[Archmonger]

Will manually resolve the following tomorrow

silk/models.py:5:1: F401 'collections.Counter' imported but unused
silk/models.py:11:1: F401 'django.db.models.F' imported but unused
project/tests/test_code_gen_curl.py:6:1: F401 'json' imported but unused
project/tests/test_code_gen_curl.py:7:1: F401 'subprocess' imported but unused
project/tests/test_code_gen_curl.py:8:1: F401 'unittest' imported but unused
project/tests/test_code_gen_curl.py:11:1: F401 'silk.code_generation.curl.curl_cmd' imported but unused
project/tests/test_view_profiling.py:1:1: F401 'random' imported but unused
project/tests/test_db.py:20:9: F841 local variable 'objects' is assigned to but never used
project/tests/test_db.py:30:9: F841 local variable 'profile' is assigned to but never used
project/tests/test_db.py:39:9: F841 local variable 'objects' is assigned to but never used
project/tests/test_db.py:55:9: F841 local variable 'profile' is assigned to but never used
project/tests/test_code.py:12:34: E741 ambiguous variable name 'l'
project/tests/test_execute_sql.py:7:1: F401 'silk.sql.connection' imported but unused
silk/views/cprofile.py:6:1: F401 'silk.models.Profile' imported but unused
silk/views/cprofile.py:7:1: F401 'silk.views.code._code_context' imported but unused
silk/views/cprofile.py:7:1: F401 'silk.views.code._code_context_from_request' imported but unused
silk/profiling/dynamic.py:5:1: F401 'functools.partial' imported but unused
project/gen.py:7:5: F841 local variable 'venetian' is assigned to but never used
project/gen.py:8:5: F841 local variable 'roller' is assigned to but never used
silk/templatetags/silk_filters.py:73:12: E741 ambiguous variable name 'l'
project/tests/test_profile_dot.py:55:13: E704 multiple statements on one line (def)
project/tests/test_profile_dot.py:80:36: F841 local variable 'filename' is assigned to but never used
project/tests/test_models.py:92:5: F811 redefinition of unused 'test_time_spent_on_sql_queries_if_has_related_SQLQueries_and_time_taken' from line 84
silk/middleware.py:30:1: E704 multiple statements on one line (def)
project/tests/__init__.py:1:1: F403 'from . import *' used; unable to detect undefined names
project/tests/__init__.py:1:1: F401 'from . import *' imported but unused
silk/model_factory.py:159:13: E722 do not use bare 'except'
project/tests/test_lib/mock_suite.py:1:1: F401 'calendar' imported but unused
project/example_app/tests.py:1:1: F401 'django.test.TestCase' imported but unused
project/tests/test_silky_middleware.py:1:1: F401 'unittest.mock.Mock' imported but unused
project/tests/test_sensitive_data_in_request.py:7:1: F401 'silk.model_factory.ResponseModelFactory' imported but unused