More closely aligns with proposed Bootstrap V4 dropdown keyboard navigation. (similar to how native select elements work)

When dropdown opens, the dropdown menu is focused.  Keyboard up/down will navigate the dropdown list. tabbing out of the dropdown will close the dropdown (and focus the next element based on normal tab flow).  hitting ESC will also close the dropdown and refocus either the button or toggle button (depending on if the button is split or not).

Also made the .sr-only "Toggle Dropdown" text a prop (toggleText) to allow for different languages.

Merge pull request #247 from tmorehouse/master

Merge in master fork

Changed feedback text block from class 'form-text' to 'form-control-feedback' to convey state.

Added ARIA role="alert" to feedback div.

Changed the target select from first child of content to querySelector() of first input element in content ref.

Fixed feedback class, & change choosing target ID

b-form-field fixed feedback class, & change choosing 'for' target ID …

Option `disabled` wasn't being factored into `formOptions()` computed result.

Option disabled wasn't being factored into formOptions()

Return disabled = false if "falsey"

* Fix validation on 'offset' prop in Popover

* Add 'targetOffset' prop to Popover

* Fix lint tests - comment edit just included to permit commit

* Fix validation on 'offset' prop in Popover

* Add 'targetOffset' prop to Popover

* Fix lint tests - comment edit just included to permit commit

This reverts commit 3222513.

Merged latest master fork