Services for Metadata and Mosaic Restrictions (previous values)

[dgarcia360]

Having to query the previous value of a mosaic restriction/metadata makes the developer have to perform extra queries in order to send one of these transactions.

With the aim of enhancing the developer experience, we could provide with separated services to create MosaicRestrictions/Metadata transactions. The services would allow creating transactions without specifying previous values, and only will work in case of having internet connection.

Idea:

1. Service: Request for required values.
2. Internal: Query for previous values.
3. Internal: Transform the values if necessary (e.g. metadata xor)
4. Internal: Create the transaction object
5. Service: Return the observable transaction object.