WIP unwatchPathsWithPrefix
add unwatchPathsWithPrefix to AppshellFileSystem
fix bugs in unwatchPathsWithPrefix
fix jslint error. skip visitor when unwatching a directory.
remove unwatchPathsWithPrefix and consilidate with unwatchPath
Merge pull request #6565 from adobe/jasonsanjose/issue-6554

Change FileWatcherDomain unwatchPath to handle directories and descendants; avoid recursive visit() for unwatching