Align table columns (and content type) to be consistent and create complete formal definitions.

Clean up tables to have only 2 columns: Name and Definition. If 'Name' by itself seems too generic, could use 'EMIX Name', or 'Element Name', or 'Entity Name'. Create formal definitions for all rows ("the formal statement of the meaning or significance of a word, phrase, etc."). Use this in schema 'documentation'. For example, currently the row containing 'PackageDiscount' has no 'Definition' column. There is only a 'Note' column stating "There may be market reasons for the price to be different than the Extended Price." and a 'Specification' column that contains info about datatype and optionality/cardinality. We need the formal definitions to reduce uncertainty and time spent discussing what is meant and enable others (end users of the spec) to understand what is meant and to put in the schema 'documentation'.