consider changing type of default_access_scope to a string

[mejohnnaylor]

why? Access scopes are strings.

Pros:

• feels a bit more consistent
• more (human) readable
• no need to bounds check the default access scope - or run into failures because we didn't
• the UML, and therefore the standard has this object as a string
• your pro here

Cons:

• defaults to empty string, we may need to enforce a "default default". The integer defaults to zero which would make the default access scope whatever was the zeroth element of the access_scopes object, which, by the way, defaults to an empty array.
• it's a late change to something supposed to have been finalled, though we actually have a small window.
• your con here

[james-peltzer]

This is fine - would like to fight about repeated string for parameter overrides of default scope later

[mejohnnaylor]

2/23 agreed to add to Smpte_handoff branch

[mejohnnaylor]

check & fix