platform: restart IDE notifications/dialogs unified
add PsiPackage.getChildren() API and corresponding extension API in PsiElementFinder.

(In Kotlin, packages really contain files rather than classes, and the new API allows to enumerate the files contained in the package, even if those files contain only top-level functions and no classes.)
Use PsiPackage.getChildren() to get the list of nodes to show. Add API in JavaCoverageExtension to allow showing summary data for elements which aren't classes or packages. Add another API to  store coverage data for some of the .class files for which we weren't able to locate the source code, and to include the coverage data for those classes in package-level summary statistics.
fix merge
IDEA-134631 (correct modality for plugin update notification)
Cleanup (dead code; duplicates; formatting)
Merge remote-tracking branch 'origin/master'