StraightenTool: hold shift/ctrl for less/more rotation per keypress

Program.cs

@@ -270,11 +270,23 @@ public class StraightenTool : ITool {
     }
 
     if (input.IsKeyPressed(Keys.Left)) {
-      photo.RotationDegreeHundredths += 10;
+      if (input.IsKeyDown(Keys.LeftControl)) {
+        photo.RotationDegreeHundredths += 100;
+      } else if (input.IsKeyDown(Keys.LeftShift)) {
+        photo.RotationDegreeHundredths += 1;
+      } else {
+        photo.RotationDegreeHundredths += 10;
+      }
     }
 
     if (input.IsKeyPressed(Keys.Right)) {
-      photo.RotationDegreeHundredths -= 10;
+      if (input.IsKeyDown(Keys.LeftControl)) {
+        photo.RotationDegreeHundredths -= 100;
+      } else if (input.IsKeyDown(Keys.LeftShift)) {
+        photo.RotationDegreeHundredths -= 1;
+      } else {
+        photo.RotationDegreeHundredths -= 10;
+      }
     }
 
     if (input.IsKeyPressed(Keys.Enter)) {