repair and update the Identifier section of the QL specification

[ginsbach]

The specification was set up so that all rules that use lowerId, simpleId, upperId were introduced in the Identifier section (aside from qualId, which is introduced before in the section on Import directives). This meant that there was one convenient central place where users could look up the allowed identifier syntax for everything.

This PR restores this principle in two ways:

1. Rules that previously circumvented some "redundant" redirections (such as type signatures using upperId directly rather than referring to classname) are changed to follow the existing behaviour of older rules.
2. Rules moduleSignatureName, signatureExpr, and parameterName and are added to the Identifier section.