changed CodeLocation so line is indexed from 0, the same way start/end are
simplified result of CodeLocation.toString() for one char long locations
added Task.name()
moved printing task execution status from PluginTask to TaskExecutor
added CollectingMessageListener
TestMessageListener extends CollectingMessageListener
added SandboxImpl.reportCollectedMessagesTo()
moved SandboxImpl to .task package
split .message package into two subpackages: message, listen
moved all messages from .task package to .task.err package