Add version to afw::table::SourceTable. Persist that version number to fits file when the table is saved, and restore when the table is restored.
Tables created and saved to disk prior to this modification will have the version number 0, by default. Tables created with the S14 version will have the version number 1.
This change is to enable a new version of slots and field naming conventions as needed by the Measurement Framework overhaul, at the same time allowing current clients of SourceTable to continue to function. The work to define and persist the slots depending on the version will be on a separate issue.
Should not appear as an alterable member of the metadata, but should be saved with the metadata and reloaded when the file is reloaded.
getVersion and setVersion methods will be used to allow clients to alter this number.