moves start() and setUserAlertManager() into the FreenetStore API
add empty start() and setUserAlertManager() in NullFreenetStore, RAMFreenetStore and SlashdotStore
change from SaltedHashFreenetStore to FreenetStore in Node
add setAltStore(FreenetStore<T> store) to FreenetStore API
LoggerHookChain: fix changing log threshold

1) we filter everything in LoggerHookChain, so we need not bother
subordinates;
2) setting threshold but not setting detailed threshold confuses subordinates;
Node: fix typo in class name
delete setAltStore() in FreenetStore API and revert some classes, add getUnderlyingStore() in FreenetStore API
Merge remote branch 'voxsim/refact-FreenetStoreAPI' into next
Delete very old back compatibility code for migration from pre-2008 saltedhash datastores.