qt(wallet): wire up HD/I2P/Tor status-bar icons

The cherry-pick of updateHDStatus/updateI2PAddress from master left the
TrianglesGUI ctor without the corresponding label_hd / label_i2p /
label_i2p_icon / label_tor_icon wiring, and trianglesgui.h missing the
function declarations. Master compiles because all four exist together.

Add the constructor blocks guarded by findChild so they no-op on
hd-on-master's narrower UI (these widgets aren't added yet) and just-
work when master merges in the I2P-UI work. Add the missing function
declarations to the header.

src/qt/trianglesgui.cpp

@@ -350,7 +350,6 @@ TrianglesGUI::TrianglesGUI(bool fIsTestnet, QWidget *parent):
     labelOnionAddress->setCursor(Qt::PointingHandCursor);
     labelOnionAddress->installEventFilter(this);
 
-    // I2P address, stacked directly above the .onion address (click to copy)
     labelI2PAddress = ui->label_i2p;
     labelI2PAddress->setVisible(false);
     labelI2PAddress->setCursor(Qt::PointingHandCursor);