[Modal] Option to make restoring focus, after a modal hides ,optional

[lubber-de]

Description

Before a modal is shown, it saves the current focussed element and restores it, after the modal was hidden again.
In some cases this might be unwanted behavior, like in Semantic-Org/Semantic-UI#6198 , where i also adopted the Testcase, so i made refocus now optional by implementing a new option restoreFocus (default true to keep current behavior)

Testcase

https://jsfiddle.net/3nmLycdr/
This was taken and adjusted from the original PR

• Make sure the viewport is small enough, so you must scroll down and the calendar won't be shown completely in the viewport
• Scroll down to the calendar
• Click either month or week buttons (so they get focus)
• Scroll down to the last calendar row. The focussed buttons should not be visible in the viewport anymore
• when the modal opens, just click cancel, so it closes again

When restoreFocus: true (behavior as before), the viewport now autoscrolls up to where the buttons are
When restoreFocus: false (set in the fiddle), the viewport stays where it is

The original PR was also forcing the code to have the element being visible to make it scroll. I don't think this should be forced, so i decided just to go with the additional setting... which exactly fixes, what the issue was originally made for.

Closes

Semantic-Org/Semantic-UI#6198

[y0hami]

LGTM

[ColinFrick]

LGTM