Update the default "filename" to have sub-folders

[Bionus]

Lots of users are confused by the name "filename", which has %md5%.%ext% as a default value. Many are not aware that Grabber can powerfully create sub-folders as needed based on the artist, character, etc.

Updating the default value would highlight this feature and make users aware more easily. %search%/%md5%.%ext% would be a pretty non-opinionated filename, for example.