Feature Request: Simplify interval definitions

[billdenney]

The number of parameters available to PKNCA is currently large, and it will only get larger as the parameter space is filled in. For that, it can be difficult for users to know what to use for the parameter. It would be helpful to make a simplified interval definition that would automatically expand into the full definition. Initial thoughts are that it would handle:

• Dosing count: "single", "multiple, steady-state", "multiple, not steady-state"
• Route of administration: "intravenous bolus", "intravenous infusion", "intravenous continuous infusion", "extravascular"
• What Clast to use ("pred" or "obs")

More should probably be added to the list. A thorough review of all parameters both currently-implemented and planned should be taken.