Add the currency to the transactions

[FlorianDubath]

For monitoring purposes, the currency should be available in the transaction record (to avoid that a transaction is accounted for multiple currency (this is a marginal case which only can happen if an address has been approved for multiple currency)

What to do:

1. on Cassandra ALTER TABLE comchain.testtransactions ADD currency text;

2. add the currency in logtodb.TMPL to the watch function as an additional field of the result object

3. modify parser.py to add the currencyif available

4. deployement:

   • send the cassandra DDL
   • update logtodb.TMPL & parser.py on the node
   • reset (on one of the node) the block number to 0 to reparse the transaction and add the currency to existing ones