Forward sorting to metasearch (ref: #990)

Except for aliased columns, that are copied verbatim in the ORDER clause.
Be backwards compatible with table_name.column_name

See https://github.com/gregbell/active_admin/pull/1766#issuecomment-12934911
Regenerate index pages documentation from source docstrings
Better warn about not editing generated documentation, and regenerate it automatically when running rake yard