Make responsive logic for side and top pane.

[alexeykomov]

Make following states for top pane (defined by viewport width):

1. Very small - 320px - only day of month and day of week are shown, without year.
2. Larger but still small - like iPhone 6 width - year is shown.
3. Larger - like iPhone 6 landscape - prev/next buttons are now lined up with other buttons.
4. Even larger - like iPad landscape - day/week/month buttons appear and side pane is of desktop style. But by default it is hidden.
5. Largest - like desktop - side pane is shown by default.