In-page tabs should use focus management

[Jono M]

On certain pages (such as /artefact/internal/index.php) form fieldsets are converted into in-page tabs which are then loaded with Javascript. Since this does not reload the page, it can be confusing for screen reader users who won't know if they have activated the link.
When the current tab is changed on pages such as this, focus should move to either the first form field or a hidden heading inside the new tab.

Note: Fixing Bug #1259387 may solve this problem if the new tab state is read out when the current tab is changed

Affects latest master (using Orca 3.9.92)

[Jono M (jonom)]

https://reviews.mahara.org/#/c/2861/