Naming of WatchTask(s)

PackageTask and PublishTask will both take a name.  WatchTask has a fixed name of 'watch'.  For better namespacing and versatility, I support naming WatchTasks.

This is a breaking change in syntax.  However, WatchTask is relatively young (see: mde/jake#122), and I searched Github but found no projects that depend on the current WatchTask syntax.  I think the change is reasonable since it brings the method arguments more in line with other Tasks.