Decrease usage of getFiles in prefetch delegate

Right now the function getFiles is called in several places, and that can affect the app's performance since that function can perform several WebService calls. We can decrease the usage with some changes:

1. In getModuleStatus, we should only call getFiles if it's really needed (getRevision or getTimemodified not implemented).
2. In getModuleDownloadedSize we could use a new handler function, getDownloadedFiles. If the handler uses component and componentId as it should, it should be able to retrieve the downloaded files without calling any WebService.
3. In removeModuleFiles we could use the same function as the previous point.