[manifest] Add icons_background_color instead of background_color (#387)

Currently, there doesn't seem to be a strong case to have background colors for individual icons. IMO, it would be better to just have a generic `icons_background_color`. If we see demand to override this on a per-icon level later, we should add `background_color` back.  Mozilla currently have no plans to support `background_color` on a per-image basis, but we want to support it on a generic basis as proposed in this PR. 
You can view, comment on, or merge this pull request online at:

  https://github.com/w3c/manifest/pull/387

-- Commit Summary --

  * Add icons_background_color instead of background_color

-- File Changes --

    M index.html (116)

-- Patch Links --

https://github.com/w3c/manifest/pull/387.patch
https://github.com/w3c/manifest/pull/387.diff

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/manifest/pull/387