Develop

@jonpday : I have extended the features 
1)To configure Prefix length. Previously it allows to only have a prefix length of 1.
2)Mutli Store: Allows the admin to set different Starting Order Numbers/Invoice/Credit Memo & Shipment  for each Store.

I have tested these features,  it works on my local.
Kindly review the code.

If you think this feature is useful please merge to Master, if not please ignore,
and delete the branch.

Thanks,
Swapna