[Qt] Show progress percent for zpiv reindex operations

`-reindexaccumulators` and `-reindexzerocoin` can take a considerable
time to complete depending on system hardware. Lets show a progress percent
 similar to `VerifyDB()` on the splashscreen.

Author: Fuzzbawls

src/main.cpp

@@ -2760,6 +2760,7 @@ bool RecalculatePIVSupply(int nHeightStart)
 bool ReindexAccumulators(list<uint256>& listMissingCheckpoints, string& strError)
 {
     // PIVX: recalculate Accumulator Checkpoints that failed to database properly
+    uiInterface.ShowProgress(_("Calculating missing accumulators..."), 0);
     if (!listMissingCheckpoints.empty() && chainActive.Height() >= Params().Zerocoin_StartHeight()) {
         LogPrintf("%s : finding missing checkpoints\n", __func__);
 
@@ -2769,6 +2770,8 @@ bool ReindexAccumulators(list<uint256>& listMissingCheckpoints, string& strError
         // find each checkpoint that is missing
         CBlockIndex* pindex = chainActive[nZerocoinStart];
         while (pindex) {
+            uiInterface.ShowProgress(_("Calculating missing accumulators..."), std::max(1, std::min(99, (int)((double)(pindex->nHeight - nZerocoinStart) / (double)(chainActive.Height() - nZerocoinStart) * 100))));
+
             if (ShutdownRequested())
                 return false;
 
@@ -2799,6 +2802,7 @@ bool ReindexAccumulators(list<uint256>& listMissingCheckpoints, string& strError
             }
             pindex = chainActive.Next(pindex);
         }
+        uiInterface.ShowProgress("", 100);
     }
     return true;
 }

src/zpivchain.cpp

@@ -259,8 +259,12 @@ std::string ReindexZerocoinDB()
         return _("Failed to wipe zerocoinDB");
     }
 
+    uiInterface.ShowProgress(_("Reindexing zerocoin database..."), 0);
+
     CBlockIndex* pindex = chainActive[Params().Zerocoin_StartHeight()];
     while (pindex) {
+        uiInterface.ShowProgress(_("Reindexing zerocoin database..."), std::max(1, std::min(99, (int)((double)(pindex->nHeight - Params().Zerocoin_StartHeight()) / (double)(chainActive.Height() - Params().Zerocoin_StartHeight()) * 100))));
+
         if (pindex->nHeight % 1000 == 0)
             LogPrintf("Reindexing zerocoin : block %d...\n", pindex->nHeight);
 
@@ -304,6 +308,7 @@ std::string ReindexZerocoinDB()
         }
         pindex = chainActive.Next(pindex);
     }
+    uiInterface.ShowProgress("", 100);
 
     return "";
 }