Refactor to store excludedModulePoms in the session (really ManagedInfo).

Provide methods for filtering POM files based on whether they're among the excludedModulePoms using the peekedPOM coordinates map along with the excludedModulePoms set.

Switch to using a set of VersionlessProjectKey instances for excludedModulePoms to allow more than one artifactId per groupId in the spec.

Don't parse effective model for excluded module POMs.