Fix bug in download_window.py. Set fixed aspect ratio for forecast images.

fixed_aspect_ratio_label.py

@@ -0,0 +1,14 @@
+from PyQt5.QtWidgets import QLabel
+from PyQt5.QtCore import QSize, Qt
+
+class FixedAspectRatioLabel(QLabel):
+    def __init__(self, parent = None):
+        super().__init__(parent)
+        self.pixmap = None
+
+    def rescale(self, w, h):
+        self.resize(QSize(w, h))
+        if self.pixmap:
+            self.setPixmap(
+                self.pixmap.scaled(
+                    self.size(), Qt.IgnoreAspectRatio, Qt.SmoothTransformation))