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).
The comment contained what to do when the depth is unknown (I took what it said to be the correct value hence returned 0 - unknown).  I can change it to -1 and document.