Remove duplicated classes ProjectExplorer::FileWatcher
and QmlProjectManager::FileSystemWatcher, create
Utils::FileSystemWatcher from them, merging the functionality.
Also use in HelpManager/Maemo, reducing the number
of QFileSystemWatcher instances (and thus, shutdown time).
If there's a library.xml file next to the qmldir file, Creator will
read that instead of trying to run qmldump on the library.
Reviewed-by: Erik Verbruggen
