When building the contextual help box, focus is set to the close button
(which now has descriptive alt text)
The help box is now inserted into the HTML immediately after the help
icon that was clicked (or after its parent if the parent is a heading)
so that the document still appears in a logical order to screen readers.

Change-Id: Ib8a10e2766038cfd32b1c6c76883f9642255639b
Signed-off-by: Jono Mingard <jonom@catalyst.net.nz>