libdeng2|Info: Added a semantic hint for script values

A '$' token in various places now indicates that the value is intended
to be parsed as Doomsday Script.

- key $: line of script
- key $= "script token"
- list < $ "script token" >
Refactor|libdeng2|ScriptedInfo: Use the semantic hint when evaluating values

Updated the test app with more examples of scriptability.