Keyboard support for links in PO line item list

[Stephanie Leary]

While fixing bug 2009092, I found that the single PO view has numerous keyboard navigation issues related to missing form labels and links used in place of buttons.

Branch coming up.

[Stephanie Leary (stephanieleary)]

Branch with numerous fixes: https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/sleary/lp2019032-lineitem-list-keyboard-support

* <a click()> is now <button type="button">
* All <button>s have a type, to avoid accidentally submitting forms using Spacebar/Enter
* Items in dropdown lists have ngbDropdownItem directive for
keyboard up/down arrow support
* Icons are now aria-hidden (except "close," which is fine as-is)
and their parent elements have ARIA labels where necessary
* Text inputs have labels instead of placeholders

[Galen Charlton (gmc)]

Tested and signed off. Signoff branch is user/gmcharlt/lp2019032_signoff.

[Galen Charlton (gmc)]

I've rebased my signoff branch in light of the patch for bug 2019117 getting merged.

[Galen Charlton (gmc)]

Given the time that has passed (and my need to push something to trigger the GitHub ng lint action), I've pushed this down to rel_3_11 on the strength of my signoff. Thanks, Stephanie!