LP#1831781: add eg-help-popover Angular component

LP#1831781: add eg-help-popover Angular component

Usage:

<eg-help-popover helpLink="https://youtu.be/dQw4w9WgXcQ"
 helptext="Helpful msg. Optional link."></eg-help-popover>

Additional placement attributes accepted. Basically wraps
ng-bootstrap's
https://ng-bootstrap.github.io/#/components/popover/examples#basic

To test
-------
[1] Go to the Angular sandbox page (/eg2/en-US/staff/sandbox) and
    verify functioning of the popovers, which display question marks.

Sponsored-by: MassLNC
Sponsored-by: Georgia Public Library Service
Sponsored-by: Indiana State Library
Sponsored-by: CW MARS
Sponsored-by: King County Library System
Signed-off-by: Cesar Velez <cesar.velez@equinoxinitiative.org>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Jane Sandberg <sandbej@linnbenton.edu>