Add functions to select all items (the typical Ctrl + a action).

sloth/core/labeltool.py

@@ -429,6 +429,10 @@ class LabelTool(QObject):
     def selectPreviousAnnotation(self):
         if self._mainwindow is not None:
             return self._mainwindow.scene.selectNextItem(reverse=True)
+    
+    def selectAllAnnotations(self):
+        if self._mainwindow is not None:
+            return self._mainwindow.scene.selectAllItems()
 
     def deleteSelectedAnnotations(self):
         if self._mainwindow is not None:

sloth/gui/annotationscene.py

@@ -260,6 +260,10 @@ class AnnotationScene(QGraphicsScene):
                 item.setSelected(True)
                 break
 
+    def selectAllItems(self):
+        for item in self.items():
+            item.setSelected(True)
+
     def keyPressEvent(self, event):
         LOG.debug("keyPressEvent %s" % event)