migrate to tox

this also requires to move default configuration files to share/ahriman.
Thus the following features have been added
* default configuration is not stored in /usr/share/ahriman/settings
* package installed via PKGBUILD now copies files from /usr
* configuration class now fallbacks to default in /usr

tox.ini

@@ -0,0 +1,35 @@
+[tox]
+envlist = check, tests
+dependencies = -e .[s3,web]
+project_name = ahriman
+
+[pytest]
+addopts = --cov=ahriman --cov-report=term-missing:skip-covered --spec
+asyncio_mode = legacy
+spec_test_format = {result} {docstring_summary}
+
+[testenv]
+deps =
+	-e .[s3,web]
+
+[testenv:check]
+deps =
+	{[tox]dependencies}
+	-e .[check]
+allowlist_externals =
+	/bin/bash
+setenv =
+	MYPYPATH=src
+commands =
+	autopep8 --exit-code --max-line-length 120 -aa -i -j 0 -r "src/{[tox]project_name}" "tests/{[tox]project_name}"
+	pylint --rcfile=.pylintrc "src/{[tox]project_name}"
+	bandit -c .bandit.yml -r "src/{[tox]project_name}"
+	bandit -c .bandit-test.yml -r "tests/{[tox]project_name}"
+	/bin/bash -c 'mypy --implicit-reexport --strict -p "{[tox]project_name}" --install-types --non-interactive || mypy --implicit-reexport --strict -p "{[tox]project_name}"'
+
+[testenv:tests]
+deps =
+	{[tox]dependencies}
+	-e .[tests]
+commands =
+	pytest