Read record with all fields in certain scope and/or namespace

[bruno]

Currently when reading a record, one can already specify what fields should be loaded.

It would be useful to extend this with the following capabilities:

• read all fields in a certain scope
• read all fields in a certain namespace

For example, if I would like to know all the version tags, I could read the record with all the fields in the version tag namespace (org.lilycms.vtag). Additionally I could specify that I only need those fields from the non-versioned scope, since version tag fields in other scopes do not make sense and are ignored anyway.

TODO: work out an API proposal for this.

[bruno]

Once the possibility to read only the fields of specified scopes is added, we can make use of it in VersionTag?.get(Id)Record to only read non-versioned fields when the specified vtag is @@versionless. See TODO note over there. Once done, the explicit check for the versionless tag in FieldFollow?.eval() could be removed.