Calendar: Picker arrows aren't flipped in RTL mode

[simeonoff]

The picker arrows don't point in the right direction when the calendar is used in RTL mode.

Here's a screenshot:

[rkaraivanov]

@simeonoff @desig9stein

After merging #910 and moving the direction context to an ancestor element instead of the story component, the issue is still present. As this is a valid application scenario (setting dir on the body/html tag itself) I'm reopening this issue.

Current state in the master branch: