qt: define QT_NO_KEYWORDS

QT_NO_KEYWORDS prevents Qt from defining the `foreach`, `signals`,
`slots` and `emit` macros.

Avoid overlap between Qt macros and boost - for example #undef hackiness
in #6421.

Conflicts:
	src/qt/addressbookpage.cpp
	src/qt/peertablemodel.cpp
	src/qt/receivecoinsdialog.cpp
	src/qt/rpcconsole.cpp

Rebased-From: d29ec6c2301e593d577126d1ca85b93307b32bf1
Github-Pull: #6433

src/qt/peertablemodel.cpp

@@ -63,7 +63,7 @@ public:
 #if QT_VERSION >= 0x040700
             cachedNodeStats.reserve(vNodes.size());
 #endif
-            BOOST_FOREACH(CNode* pnode, vNodes)
+            Q_FOREACH (CNode* pnode, vNodes)
             {
                 CNodeCombinedStats stats;
                 stats.nodeStateStats.nMisbehavior = 0;
@@ -91,7 +91,7 @@ public:
         // build index map
         mapNodeRows.clear();
         int row = 0;
-        BOOST_FOREACH(CNodeCombinedStats &stats, cachedNodeStats)
+        Q_FOREACH (const CNodeCombinedStats& stats, cachedNodeStats)
             mapNodeRows.insert(std::pair<NodeId, int>(stats.nodeStats.nodeid, row++));
     }
 
@@ -219,9 +219,9 @@ const CNodeCombinedStats *PeerTableModel::getNodeStats(int idx)
 
 void PeerTableModel::refresh()
 {
-    emit layoutAboutToBeChanged();
+    Q_EMIT layoutAboutToBeChanged();
     priv->refreshPeers();
-    emit layoutChanged();
+    Q_EMIT layoutChanged();
 }
 
 int PeerTableModel::getRowByNodeId(NodeId nodeid)