Allow parsing of padded numerical strings

[antonydenyer]

Padded numerical strings are no longer accepted

A bug was introduced in https://github.com/web3j/web3j/pull/1679

Whilst not producing a padded string may be desirable, you should certainly accept them. When calling Numeric.decodeQuantity an exception is now thrown if you pass a padded string. I think the Robustness Principle should be adhered to. For instance, an rpc endpoint may produce a padded string.