Wrap cover image content in a DIV

[r-a-y]

If a plugin is using the 'bp_member_before_header' hook or the 'bp_before_group_header' hook to inject some content before the header, the content is not visible in the cover image header.

Problem is we need to wrap a container around the entire cover image block instead of using the existing #item-header DIV.

[imath]

Thanks a lot for this catch @r-a-y :)

I've just tested there were no impact on the javascript part when setting/deleting the cover image. And everything is ok. So for me it's good to go.

[r-a-y]

Thanks for the feedback, imath!

[r-a-y]

In 10290:

Cover Image: Wrap cover image block in a DIV.

Fixes a potential display issue when plugins try to use the
'bp_after_member_header' or 'bp_before_group_header' hooks to inject
content before the cover image.

Fixes #6673.