Follow DCP0012 once activated

[davecgh]

This is currently being done using an extra getblockchaininfo RPC call any time votes may need to be created. While not ideal, and caching of previously observed active and lockedin statuses could be utilized, this is the bare minimum needed to make wallet follow the DCP0012 hard fork if it is approved.

[davecgh]

Tested via simnet by applying the following patch to dcrd in order to make the agenda inactive and allow it to be voted in:

diff --git a/chaincfg/simnetparams.go b/chaincfg/simnetparams.go
index ebb261288..1a5c3d3d3 100644
--- a/chaincfg/simnetparams.go
+++ b/chaincfg/simnetparams.go
@@ -473,7 +473,7 @@ func SimNetParams() *Params {
                                                IsNo:        false,
                                        }},
                                },
-                               ForcedChoiceID: "yes",
+                               //ForcedChoiceID: "yes",
                                StartTime:      0,             // Always available for vote
                                ExpireTime:     math.MaxInt64, // Never expires
                        }},

Output of a single vote subsidy at height 1103 (one block before activation) and a vote with the new subsidy in the mempool:

$ ./ctl getblockhash 1103 | ./ctl getblock - true true | jq '.rawstx[1].vin[0].amountin'
73.87865779
$ ./ctl getrawmempool false votes | jq -r '.[0]' | ./ctl getrawtransaction - 1 | jq '.vin[0].amountin'
82.19000679

Output of a single vote subsidy at height 1104 (activation height):

$ ./ctl getblockhash 1104 | ./ctl getblock - true true | jq '.rawstx[1].vin[0].amountin'
82.19000679