Have PluginRequestApplicator build the script classloader scope whether there are plugins or not.

+review REVIEW-5154
Inject VersionMatcher instead of manually constructing.

+review REVIEW-5154
Fix formatting of XML under comparison.
Fix sample tests after package rename.
Don't need to explicitly wire the start param config to plugin dependency resolution.

This happens implicitly in the dependency management bootstrapping.

+review REVIEW-5154
Add test case for using buildscript {} and plugins {} and classes from both being visible to buildscript.

+review REVIEW-5154
Break out story for visual feedback during plugin resolution.

+review REVIEW-5154
Expand improved classloading of non-declarative plugins to include not implicitly inheriting classes from the parent scope.

+review REVIEW-5154
Break out stories for avoiding redundant downloads of plugin implementation modules and for diagnostics of conflicts between plugin implementations.

+review REVIEW-5154
Utility for unpacking an iterable of factories.
Avoid unnecessary creation of interm loaders for scope where the there are single additions to local/export that have the effective parent.

+review REVIEW-5154
Avoid direct path to parent in scope loader if one of the other loaders in the scope already has the scope parent as a parent.

+review REVIEW-5154