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).
Access to the users private resource path (derived from the
settings path) has been used in quite some places, so it's
worth moving it to the core interface centrally.
Reviewed-By: Thorbjorn Lindeijer
