Cnx-db

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- Add a SQL query to obtain the 'head' version of content. The head
is the last publication made for that content regardless of whether
it is in a publicly viewable state.

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- Adds fulltext search fixes and speedups.

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- Fix the documentation for Pyramid integration properties.
- Fix the HTML reference resolver for cases where the moduleid is found
in the resource filename.

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- Transition the following Pyramid integration properties:
``registry.engines`` and ``registry.tables``. These are now moved to
``request.get_db_engine()`` and ``request.db_tables``.
This favors the recommended pattern of using request methods and attributes
for hooking into the current thread local variable space.

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- Fix shred_collxml code to insert the ``trees.latest`` value.
The fix includes a migration to ensure all ``trees.latest`` values are
set to true, which should be the casee for all legacy content.
See https://github.com/Connexions/cnx-db/issues/120 for issue details.

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- Pin to a specific version of sesssion_exec when testing.
- Allow the Google Analytics (GA) code column to stay the same type,
but contain multiple GA codes. Adjustments to queries make this
an array of GA codes based on space separated list of codes.
- Adjust the books containing this page query to:
- Provide a sorted list of authors and the detailed person info
- Provide the shortid