[darc/maestro++] Dependency update + add handling should be generic and consistent

[mmitche]

The update and add dependencies operations on the git file manager use different handling for:

• Adding (uses new updaters, but these can't be used for update)
• Updating (uses special handling for global.json, but not the generic known updater function)
• Script files are handled at the Remote level rather than the file manager level.

This should be consistent.

In addition, this is a good time to change how we specify 'well known' types. These should be able to be specified in the Version.details.xml file. So darc would read that and choose an updater based on the type. The default should be Versions.props.

[mmitche]

/cc @jcagme

[premun]

This is getting in my way and I will handle this as part of the backflow change

[premun]

Ah, I take it back, this one looks more work and won't get me what I need anyway.