FilenameService to keep in sync title, short name and filename

For filesystem connectors (WebDAV, WSS, CMIS) we need a coherent view (that users expect) between the various filenames, URL components, titles, etc.

Add a new FilenameService and some listeners to make sure that in most cases a document's title, short name and filename are kept in sync. This also applies (in a simpler way) to folders.