New method ConfigurationManager.resetToDefault(configurationKey)

This method is useful when after an update we need to reset default configuration values
to fix problems that we don't want to continue even though they've been fixed
with simple default configuration fixes.

some small refactors.
TransferManager using slf4j
slf4j on TorrentUtil
Show me why you can't flush disk crawl cache
sl4f on TorrentFetcherDownload