DOC: added documentation from old wiki

src/doc/Data-Model.md

src/doc/Glossary.md

src/doc/Permissions.rst

src/doc/administration.rst

src/doc/administration/configuration.rst

src/doc/administration/curl-access.rst

src/doc/administration/server_side_scripting.rst

src/doc/concepts.rst

src/doc/entities.png

src/doc/index.rst

src/doc/roles.md

src/doc/specification/AbstractProperty.md

src/doc/specification/Authentication.md

src/doc/specification/Datatype.md

src/doc/specification/Fileserver.md

src/doc/specification/Paging.md

src/doc/specification/Record.md

src/doc/specification/RecordType.md

src/doc/specification/Server-side-scripting.md

src/doc/specification/Specification-of-the-Entity-API.md