Add support for new MeaningsTable type in hdfm-common #284

Overview

In hdmf-dev/hdmf-common-schema#91 the following key changes were made:

1. added MeaningsTable as a new type
2. updatedDynamicTable to add a sub-group for storing instances of MeaningsTable

With this design, each column in a DynamicTable may optionally have a corresponding MeaningsTable.

Approach

• Update schema in AqNWB to support the latest hdmf-common schema. See http://nwb.org/aqnwb/nwb_schema_page.html for instructions.
• Add new class for representing MeaningTable. See http://nwb.org/aqnwb/registered_type_page.html for instructions.
• Update DynamicTable::initialize implement the required schema changes, in particular, creating the required meanings_tables group
• Update DynamicTable to add the required macros (e.g., DEFINE_UNNAMED_REGISTERED_FIELD) for reading and creating MeaningsTable objects
• Optional: Add convenience methods in DynamicTable to simplify creation of MeaningsTables for a column
• Update the user-docs to add a tutorial on using DynamicTable and MeaningsTable, incl., adding an example in tests/examples
• Add comprehensive unit tests for the new features
• Update the CHANGELOG