Update ReceiptStorage.java

The previous createFromCSV(String csv) method didn't work.

Some issues/questions : 
1)As I commented in the code OpenCSV library reads from CSV files as Doubles, you don't parse BigDecimals but Doubles, so there's the possibility of having a loss of data precision.
2)Are we sure that everything else stops when writing/reading to the CSV file? I mean if we write like 100000 receipts and load them back will the trading system wait for this higher latency operation? Should we put a Thread.sleep() somewhere? Can we have corrupted or incomplete data in RAM if we don't properly wait for this operation? Maybe it's already fine now..
3) According to the signatures of methods to write and read back from Csv file, we can specify where to read from but not where to write to...isn't this nonsense?
Merge pull request #49 from NeoSephiroth/patch-4

Update ReceiptStorage.java