FS: StorageCachedBlockDevice should live in storage-device

[roblabla]

StorageCachedBlockDevice is truthfully a fancy StorageBlockDevice<CachedBlockDevice>. The only difference between the two is that it has a special read method that ~~is totally broken~~ handles misaligned blocks in a somewhat efficient way. There's no reason why this function couldn't be implemented on StorageBlockDevice.

@Orycterope since you're going to be fixing the broken read method anyways, I think you should move it to storage_device at the same time.

[Orycterope]

yep, that was my plan all along