Adopt modern packaging

[yakky]

• drop python 2 / Django < 2.2 / django CMS < 3.7
• bumpversion
• towncrier
• github actions
• pre-commit
• github templates
• add basic wizard tests

Fix #362 Fix #363 Fix #364 Fix #370 Fix #8

[codecov[bot]]

Codecov Report

Merging #373 into develop will increase coverage by 1.67%. The diff coverage is 95.72%.

@@             Coverage Diff             @@
##           develop     #373      +/-   ##
===========================================
+ Coverage    92.78%   94.46%   +1.67%     
===========================================
  Files            7        7              
  Lines          610      614       +4     
  Branches       121      128       +7     
===========================================
+ Hits           566      580      +14     
+ Misses          17       10       -7     
+ Partials        27       24       -3     

Flag	Coverage Δ
#unittests	94.46% <95.72%> (?)

Impacted Files	Coverage Δ
djangocms_installer/config/internal.py	86.20% <42.85%> (-0.46%)	:arrow_down:
djangocms_installer/config/ini.py	90.41% <91.66%> (+2.09%)	:arrow_up:
djangocms_installer/install/__init__.py	95.34% <94.11%> (-0.11%)	:arrow_down:
djangocms_installer/config/__init__.py	97.17% <96.90%> (+5.24%)	:arrow_up:
djangocms_installer/django/__init__.py	92.48% <98.24%> (-0.07%)	:arrow_down:
djangocms_installer/config/data.py	100.00% <100.00%> (ø)
djangocms_installer/utils.py	100.00% <100.00%> (ø)

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[github-actions[bot]]

Coverage decreased (-10.2%) to 87.075% when pulling 522066ca82c54ca237cce73fedf1eb51434721f9 on feature/issue-364-modern-packaging into d964fc398bceedd24ed01aa5f6388fe1e49c4c56 on develop.