Processed transactions

I am worried about the level of testing. Some of the history tests have been commented out because I completely changed the api. I will write them back in.

The full test suite passes, but I'm guessing there are a handful of latent bugs in this PR.

I changed the api according to have more descriptive wallet transactions. Also less confusing. Calling /wallet/siacoins now returns a list of transaction ids - the ids of the transactions that were created to send the siacoins.