* Add dropright (right placement for our dropdown)

* Add dropleft

* moves drop left arrow to the left

* Add .modal-dialog-centered for optional vertically cenetered modal

Fixes #23638

* adds modal-dialog-centered class to docs and removes margin to avoid generating a vertical scrolling

* mention limitations

* fix aria attr

* Add `width: 100%` to the .modal-content for the centered version. Adding it here to avoid adding another selector by limiting it to the centered modal modifier.

* Add information about the fact we do not use Popper.js for Dropdown contained in navbars

* Update dropdowns.md

* Update dropdowns.md

Fixes #24503 by manually calling the border-radius instead of using the mixin.

- Drops the Team page for privacy and accuracy. I don't want to pressure folks into feeling committed to the project through a page like this, and it also doesn't allow folks any privacy option (as you can hide org membership on your GitHub profile).
- Moves the History page into an Overview page, which includes an updated history page and a quick team blurb at the top.
- Added redirects to the new Overview page from Team and History

`js-compile` and `js-minify` tasks already call their "children" tasks.

We don't support Opera 12, and Firefox's property was the unprefixed one.

Merge branch 'btn_input_split_variables' of https://github.com/isychev/bootstrap into isychev-btn_input_split_variables