Core terminal update

[Vedant1]

Changed internal data abstraction (ordered dictionary) into nested ordered dictionaries so it can handle multiple tables ingested - each table is its own ordered dictionary.

Updated metadata.py to handle the extra level of collections (the internal data abstraction)
Updated sqlite.py to loop through all tables to create them
Updated core.py to allow these new plugins to be loaded and separated the use of readers/writers in transload()

Added yaml/toml file readers and table_plot file writer in format used by core terminal.

• readers use add_rows() and writers use get_rows() which inputs the collection to be formatted for a file output

Edited coreterminal.py with 2 workflows on loading readers, writers and a backend (sqlite)

Added capability to store table relations through PK/FK columns
Updated sqlite.py to handle these relations