Suggested addition to getTxHistory

[dabura667]

In addition to tagLowFees which adds a 'lowFees' attribute to transactions,
please add tagFeeDust which will add a 'isFeeDust' attribute to transactions.

tagFeeDust would do the following:

1. Determine the current fee levels.
2. Determine the type of wallet (single? x of y?)
3. Estimate the size of an input for the wallet type (148 bytes for single, 73 * m + 34 * n + 49 for m-of-n)
4. Multiply superEconomy fee by size estimate of 3.
5. If the value of the UTXO is less than the value from calculating step 4, show the user in Copay a message that says "This bitcoin is too small for current fee rates. Using it would cost more in fees than not using it at all. Please wait until fees go down to use."

The edge cases that could be problematic (since this is really an attribute to a utxo but we're sticking it on a transaction) is if two outputs of a single transaction are both sent to our wallet. Would such a transaction be treated as two "transactions" in BWS terms?