R1:4699c2901765

Fix calendar z-index and Conpherence/Calendar integration

Summary:
Fixes T7975. Long ago, this element looked like this when you expanded it:

```
+-------------------+
| 3 4 5 6 7 X |
| 8 9 1 2 3 4 5 +---+
| 6 7 8 9 1 2 3 |
| 4 5 6 7 |
+---------------+
```

That was why the icon needed a z-index. See T5880. @chad fixed this a while ago so it looks like this:

```
+---------------+
| 3 4 5 6 7 | X
| 8 9 1 2 3 4 5 |
| 6 7 8 9 1 2 3 |
| 4 5 6 7 |
+---------------+
```

...but we never…