Rename gist instances to use our naming convention

[rjyounes]

Naming convention from style guide:

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• Leading underscore
• An infix consisting of the name of the class that is the most specific rigid class the instance belongs to
• A single underscore
• The name of the instance, with spaces and hyphens replaced by underscores (no camelcasing) and only alphanumeric characters and underscores allowed
• Leave case as it is

A "rigid" class is one that the instance inherently belongs; it is part of the essence of the object, which would not be the same object if it did not belong to this class. A non-rigid class may be temporary and/or express a role or relationship; for example, Child, Patient, Employee. The notion of rigid classes originates in OntoClean.

The "most specific rigid" class is the rigid class that the instance most directly belongs to.

For example, given the class hierarchy Living Thing > Person > Student, where the first two classes are rigid and the third is not, the name for Sir Tim Berners-Lee is _Person_Sir_Tim_Berners_Lee.

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None of the gist individuals for units and durations follow this convention.

We should also use the namespacing convention we use for client projects - I.e., we should use https://taxonomies.semanticarts.com/gist/ (gistx). As a result we would have, for example, gistx:_DurationUnit_minute. See issue #305.

Original terms can be deprecated to make this a minor change.

[uscholdm]

This is a good idea, though it will make all the IRIs long and clunky.

[rjyounes]

Submit one PR for #370, #526, and #556.

[rjyounes]

Existing terms need to be added to a gistDeprecated.ttl file - which doesn't currently exist because we just removed it for the major release.