Improve XMvnWorkspaceReader.findVersions()

If requested artifact cannot be resolved then return empty list of
available versions.  If artifact is resolved to a compat version then
return that version.  Otherwise return "SYSTEM".
Map Ivy artifact types to Aether classifiers
Install effective POMs when publishing Ivy files
Allow specifying custom providers for IvyResolver
Add test dependency on EasyMock
Generate equals() and hashCode() in request API beans
IvyResolver: return null for non-existent POM
[test] Implement basic Ivy resolver test
Implement artifact adapter
Use internal artifact representation instead of Aether
Add artifact scope and stereotype getters and setters
Remove properties from artifact API
Change argument order in DefaultArtifact constructor
Convert DefaultArtifact so self-contained artifact implementation
[test] Add unit test for DefaultArtifact
Remove dependency on Aether API from POM files
Simplify code related to Artifact
[test] Add slf4j-cimple to test dependencies
Make XMvnHomeClassLoader import XMvn Artifact instead of Aether Artifact