Remmediate [PIH-01M] Inexistent Support of Manual Seller Configuration

[zajck]

Closes #728

Based on #746 which should be reviewed and merged first.

Instead of backfilling the data at the initialization time, seller salts are now generated

• when a seller is created for new sellers
• dynamically the first time the new collection is created for existing sellers.
  • Existing sellers can also manually set it by calling updateSellerSalt

Due to the changes in #746 it will be possible that the same wallet creates multiple seller ids. It's also possible that already now there exist seller accounts with the same creator address. To avoid collisions, seller salt is now derived from the admin address and the user-supplied salt.
Since this is a user-defined value, we cannot just pick it on the sellers' behalf.

Two view methods were added to check if the chosen salt will result in successful clone creation:

• isSellerSaltAvailable can be used before calling createSeller, createNewCollection (for sellers from before v2.3.0 which might not have seller salt initialized yet) or updateSellerSalt
• calculateCollectionAddress can be used to get both the expected collection address and its availability.

[coveralls]

coverage: 99.571% (+0.005%) from 99.566% when pulling 7c277e7 on audit_v2_3_0_pih_01_m into 58dddcb on main.

[levalleux-ludo]

@zajck I've left a small question

[albertfolch-redeemeum]

LGTM