Upgrade project to Django 3/Python 3.7

[Xpirix]

• Upgrade Django project according to this issue: #54
• The changes on the current PR is based on this existing PR: #257

Please find below the version of each pip package according to pip freeze:

amqp==5.2.0
asgiref==3.7.2
backports.zoneinfo==0.2.1
billiard==3.6.4.0
cached-property==1.5.2
celery==5.2.7
certifi==2023.11.17
chardet==3.0.4
click==8.1.7
click-didyoumean==0.3.0
click-plugins==1.1.1
click-repl==0.3.0
coreapi==2.3.3
coreschema==0.0.4
defusedxml==0.7.1
Django==3.2.11
django-annoying==0.10.6
django-auth-ldap==4.3.0
django-bootstrap-pagination==1.7.1
django-celery-beat==2.3.0
django-debug-toolbar==3.2.4
django-extensions==3.2.3
django-haystack==3.2.1
django-preferences==1.0.0
django-ratings @ git+https://github.com/gelo-zhukov/django-ratings.git@fb5495d7a9a3aec9800f12dff58803ff68a4c753
django-rest-auth==0.9.5
django-rest-multiple-models==2.1.3
django-simplemenu @ git+https://github.com/elpaso/django-simplemenu.git@4d318522104ed53a5e62ee3bf4180119ef025f6d
django-sortable-listview==0.43
django-taggit==4.0.0
django-taggit-autosuggest==0.4.1
django-taggit-templatetags==0.2.5
django-templatetag-sugar @ git+https://github.com/metamatik/django-templatetag-sugar.git@33bc10cc560521f7932c66e677b32276e4ad6915
django-timezone-field==5.1
django-tinymce==3.4.0
djangorestframework==3.11.2
drf-yasg==1.17.1
feedjack @ git+https://github.com/dimasciput/feedjack.git@369bb402840db46a3fbcfe66deaba322fb7d1bbd
feedparser==5.2.1
idna==2.10
importlib-metadata==4.13.0
inflection==0.5.1
itypes==1.2.0
Jinja2==3.1.2
kombu==5.2.4
Markdown==3.2.1
MarkupSafe==2.1.3
packaging==23.2
Pillow==9.5.0
prompt-toolkit==3.0.41
psycopg2==2.9.9
pyasn1==0.5.1
pyasn1-modules==0.3.0
python-crontab==3.0.0
python-dateutil==2.8.2
python-ldap==3.4.4
pytz==2023.3.post1
PyWavefront==1.3.3
requests==2.23.0
rpc4django @ git+https://github.com/elpaso/rpc4django.git@4cd47103654833f6e5931e0fe807ddf3a207d246
ruamel.yaml==0.18.5
ruamel.yaml.clib==0.2.8
six==1.16.0
sorl-thumbnail==12.9.0
sorl-thumbnail-serializer-field==0.2.1
sqlparse==0.4.4
typing_extensions==4.7.1
tzdata==2023.3
uritemplate==4.1.1
urllib3==1.25.11
uWSGI==2.0.23
vine==5.1.0
wcwidth==0.2.12
Whoosh==2.7.4
zipp==3.15.0

[codecov-commenter]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (998e0b5) 36.06% compared to head (04c5ffe) 36.52%.

Files	Patch %	Lines
qgis-app/plugins/tasks/update_feedjack.py	66.66%	2 Missing :warning:
qgis-app/plugins/tasks/generate_plugins_xml.py	75.00%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #310 +/- ## ========================================== + Coverage 36.06% 36.52% +0.45% ========================================== Files 111 119 +8 Lines 4899 4939 +40 ========================================== + Hits 1767 1804 +37 - Misses 3132 3135 +3 ```

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[dimasciput]

@Xpirix can you fix the conflicts please

[Xpirix]

The conflicts are resolved. Thanks @dimasciput

[dimasciput]

done in https://github.com/qgis/QGIS-Django/pull/374