ScriptInfo: generalize input/output adding methods

This change also fixes a bug where the return value
output item was not actually marked as ItemIO.OUTPUT.
ScriptInfo: change clearInputs to clearParameters

The method now clears out both inputs and outputs.
ScriptInfo: rename parseInputs to parseParameters

This change is in preparation for outputs to parsed the same way.
ScriptInfo: update parseParameters javadoc

The new javadoc describes the new intended syntax options.
ScriptInfo#parseType: load classes with ClassUtils
ScriptService: add parseType(String) method

This method converts a string (which could be a simple class name
or other abbreviation, or might be a fully qualified class name)
into a Java class object.
ScriptInfo: use ScriptService#lookupClass method

By delegating class resolution to the script service, we avoid
each ScriptInfo instance having its own type lookup table.
fixup! ScriptInfo: update parseParameters javadoc
ScriptInfo: simplify '@' scanning code
WIP: ScriptInfo: first cut at new parameter syntax