HBD stabilizer update

Now that HBD has declined to 1 USD (though, likely more due to market factors than as a result of the stabilizer), the stabilizer has begun returning HBD to the DAO as-is rather than using it to buy HIVE.

In addition, the stabilizer will now use HIVE to purchase HBD when it is possible to do so for less than 1 USD, and return that HBD to the DAO instead. This maximizes the value in terms of number of HIVE (including those that might be created by converting undervalued HBD) taken off the market and sequestered into the DAO account.

HIVE in the stabilizer account will come from donations, beneficiaries, etc. In the future we may also convert HBD to obtain HIVE, but this is not currently implemented (for reasons discussed in previous posts).

100% beneficiary to @hbdstabilizer