Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/584e33a45f6b
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #20536 from KevinGrandon/bug_1022414_dragdrop_fixes

Bug 1022414 - [Vertical] Dragdrop improvements

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https://hg.mozilla.org/integration/gaia-central/rev/764670b6ec93
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1022414 - [Vertical] Dragdrop improvements r=crdlc

Many improvements to drag drop in vertical homescreen including:
* Ignores dividers during distance calculation and relys only on icons or placeholders to determine proper drop target.
* Render a row of placeholders after the last divider. This ensures we have a valid drop target even if we ignore dividers.
* The last row of placeholders have a smaller size are are only for divider creation.
* Buffers from/to indexes to have slightly better performance and prevent the stuck icon situation.

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https://hg.mozilla.org/integration/gaia-central/rev/7777da9ed5b2
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #20522 from KevinGrandon/bug_1021343_dual_homescreen_entries

Bug 1021343 - [Settings] Duplicated Homescreen entry

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https://hg.mozilla.org/integration/gaia-central/rev/958aeef31aff
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1021343 - [Settings] Duplicated Homescreen entry r=crdlc r=yurenju
Bumping manifests a=b2g-bump