[Tests] Fully reconfigure tox to automate everything

The following separate testenvs are defined (with their commands to run):

  tox              Run test suite
  tox -e lint      Run flake8 tests (including mypy and bandit)
  tox -e security  Run safety to check for vulnerable dependencies
  tox -e docs      Run sphinx to build documentation
  tox -e build     Run poetry to build sdist and bdist_wheel

tox.ini

 [tox]
 skipsdist = True
-envlist = default
+skip_missing_interpreters = true
+envlist = py37,py38
 
-[testenv:default]
+[testenv]
 whitelist_externals = poetry
-    pytest
 skip_install = true
-commands = pytest --pylama --cov=biscuit {posargs} biscuit/core/
-setenv =
-    TEST_SCREENSHOT_PATH = {env:TEST_SCREENSHOT_PATH:}
-    TEST_SELENIUM_HUB = {env:TEST_SELENIUM_HUB:}
-    TEST_SELENIUM_BROWSERS = {env:TEST_SELENIUM_BROWSERS:}
-    TEST_HOST = {env:TEST_HOST:}
-
-[pylama]
-linters = pycodestyle,pyflakes,radon
-
-[pycodestyle]
+envdir = {toxworkdir}/globalenv
+commands_pre = poetry install
+commands =
+    poetry run python manage.py compilemessages
+    poetry run python manage.py yarn install
+    poetry run python manage.py collectstatic --no-input --clear
+    poetry run coverage run -a -m pytest {posargs} biscuit/core/
+    poetry run coverage report --include='*/biscuit/core/*'
+passenv =
+    TEST_SCREENSHOT_PATH
+    TEST_SELENIUM_HUB
+    TEST_SELENIUM_BROWSERS
+    TEST_HOST
+
+[testenv:lint]
+commands = poetry run flake8 {posargs} biscuit/core/
+
+[testenv:security]
+commands = poetry run safety check --full-report
+
+[testenv:build]
+commands_pre =
+commands = poetry build
+
+[testenv:docs]
+commands = poetry run make -C docs/ html {posargs}
+
+[flake8]
 max_line_length = 100
-ignore = E501
-
-[autopep8]
-jobs = 0
-aggressive = true
+exclude = migrations,tests
+ignore = E231
 
 [mypy]
 plugins = mypy_django_plugin.main
+python_version = 3.8
+platform = linux
+show_column_numbers = True
+follow_imports = skip
+ignore_missing_imports = True
+cache_dir = /dev/null
 
 [mypy.plugins.django-stubs]
 django_settings_module = biscuit.core.settings
@@ -34,5 +54,6 @@ django_settings_module = biscuit.core.settings
 DJANGO_SETTINGS_MODULE = biscuit.core.settings
 
 [coverage:run]
-omit = */migrations/*
+omit =
+    */migrations/*
     */tests/*