Added --maven-overrides parameter for ceylon/ceylon-module-resolver#81
CMRTest: use ":" as group/artifact separators for Maven imports ceylon/ceylon-module-resolver#81
LazyPackage: use the overloads list when looking up a class with a signature

because the compiledDeclarations list may be empty
CMRTest: added test for maven overrides ceylon/ceylon-module-resolver#81