-`useMetadata(did)` : it gets the DDO and then loads all the values (title, metadata etc)
-`useMetadata(ddo)` : it uses the passed DDO and the loads all the values, in case you already got a list of DDOs, so you don't have to fetch the DDO once again
-`useMetadata()` : loads nothing, useful for using functions like `getPrice` or `getPool` with minimal calls