feat(dropdown): Automatically adjust direction if partially outside screen

[slavik990]

We can set dropdown position via class ("pointing"), but sometime it cannot be placed on screen. In this case I think it should change default position to other

[edcarroll]

I think because this isn't the default behaviour of the dropdown component (in the base semantic UI library), this should be added as a separate configuration option, such as [autoPosition], that sets the upward class and changes the transition accordingly. Will put this in the next release.

[mcosta74]

Does this Semantic-Org/Semantic-UI#4211 (released in v2.2.11) fix the issue ??

[edcarroll]

@mcosta74 looks like that PR updates the dropdown JS code, so won't affect behavior here unfortunately