Support for data source templates

[mwatts15]

Data sources can have user-specific values associated with them like connection details and access date. Some of these values are only resolved at translation-time (i.e., when the data source is being used) and not relevant to reproduction (e.g., user name, local proxy host/port) while others may be useful for reproduction (e.g., access date, run-time computer specifications, time of execution). Such values would simply be a part of the data source, and recorded in the graph, if the source wasn't to be shared, but this sort of shareable value may apply even for resources which are shared. Furthermore, creating a class for each such data sources would create too many classes and, properly done, would require duplicating several attributes such that they apply to a class as well as an instance of a source.

The suggestion of this issue is to create a 'templatedBy' relation which captures this kind of specialization between data sources. This would be used in conjunction with the DataSource:source relation or may be created as a sub-property of that DataSource:source (and thus take its place).

• There is already logic for 'capabilities' which resolve user-specific values at translation-time for data sources. This should be utilized and/or expanded to fill in shareable translation-time values as well, although the data sources themselves would retain the logic for filling the template values in where they belong.
• The OWM.translate method would need to know which sources are templates in order to create a new non-templated version for translation purposes.
• Data sources would need to have some kind of template/non-template marker--probably a sub-class of DataSource is best.
• The fact that a data source is a template should be accessible in the graph