Cleanup and restructuring of documentation.

.gitignore

admin_doc/source/_static/gracedb-nav-style.css

admin_doc/source/_templates/layout.html

admin_doc/source/client_release.rst

admin_doc/source/conf.py

admin_doc/source/dev.rst

admin_doc/source/index.rst

admin_doc/source/new_event_subclass.rst

admin_doc/source/new_gracedb_instance.rst

admin_doc/source/new_pipeline.rst

admin_doc/source/new_server_feature.rst

admin_doc/source/ops.rst

admin_doc/source/robot_certificate.rst

admin_doc/source/shibbolized_client.rst

admin_doc/source/user_permissions.rst

doc/source/conf.py

doc/source/index.rst

doc/source/ref_manual.rst

doc/source/responding_to_lvalert.rst

doc/source/tutorials.rst