Create a new UTXO Provider and the ability to generate spends (from free standing outputs).

I have create a store coin selector that can be used to create spends from the full store.  I changed a few things internally so that send requests complete correctly. 

I'm not sure if the wallet side of the functionality is as you expected (the fromBlockStore)?  

Review and suggestions for changes/improvements welcome  :)
Thanks.
K

1) Update the Full stores to return StoredTransactionOutput's.
2) Created another coin selector (and abstract class that sub systems can implement) to get candidates from the wallet directly via the store.
3) Updated MySQL field blob size .  It's capacity isn't sufficient (if this field is ever use in future).
4) Updated internal objects to be able to cope with a null parent tx (spend standalone outputs).
Another thought - if this returned List<TransactionOutput> instead of List<StoredTransactionOutput> then the wallet itself could implement UTXOProvider (it is one after all!) and then the default value of the utxoProvider field can be "this". FreeStandingTransactionOutput would then either move into the store package. I guess we could rename it to be "TransactionOutputFromDB" to be a little clearer.

Having the wallet be its own UTXO provider seems conceptually cleaner and means there's no special mode-switching code going on. I'm not sure how easy it is but it doesn't feel too hard.