[Docs] Merge handbook content from AlekSIS-Handbook

docs/Makefile

docs/admin/00_index.rst

docs/admin/10_basic.rst

docs/admin/25_concepts.rst

docs/admin/30_configure.rst

docs/admin/40_preferences.rst

docs/conf.py

docs/index.rst

docs/make.bat

docs/user/00_index.rst

docs/user/10_overview.rst

docs/user/20_lesson.rst

docs/user/25_group_roles.rst

docs/user/30_statistics.rst

docs/user/40_export.rst

pyproject.toml