Missing elastic boundaries

[perlatus]

Boundaries should be elastic.

• When you zoom in too far, it should let you—but then shrink back to the smallest zoom size.
• When you zoom out too far, it should let you—but then grow to fill the screen.
• When you pan past the boundaries, it should let you—but then pan until the viewport boundaries are back.
• ...

Probably depends on #1.

Should have a delay so that it only animates when not between pinch-zooms.

[perlatus]

Should be similar in appearance to how images in iOS work. For example, how the narwhal reddit app does bounce back.