Hide emoji panel if it's not under the mouse cursor

fixes #254
fixes #246

include/emoji/Panel.h

@@ -37,8 +37,16 @@ signals:
         void emojiSelected(const QString &emoji);
 
 protected:
-        void leaveEvent(QEvent *event);
-        void paintEvent(QPaintEvent *event);
+        void leaveEvent(QEvent *event) override
+        {
+                emit leaving();
+                QWidget::leaveEvent(event);
+        }
+
+        void paintEvent(QPaintEvent *event) override;
+
+signals:
+        void leaving();
 
 private:
         void showCategory(const Category *category);

include/emoji/PickButton.h

@@ -18,6 +18,7 @@
 #pragma once
 
 #include <QEvent>
+#include <QTimer>
 #include <QWidget>
 
 #include "FlatButton.h"
@@ -37,6 +38,7 @@ signals:
 
 protected:
         void enterEvent(QEvent *e) override;
+        void leaveEvent(QEvent *e) override;
 
 private:
         // Vertical distance from panel's bottom.
@@ -46,5 +48,6 @@ private:
         int horizontal_distance_ = 70;
 
         QSharedPointer<Panel> panel_;
+        QTimer hideTimer_;
 };
 } // namespace emoji