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

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https://hg.mozilla.org/integration/gaia-central/rev/0c4121251a84
Author: Tzu-Lin Huang <dwi019@gmail.com>
Desc: Merge pull request #25639 from dwi2/bug1091353

Bug 1091353 - Home key and Power key should be only handled by System App r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/e9bac0f0d64f
Author: Tzu-Lin Huang <tzhuang@mozilla.com>
Desc: Bug 1091353 - Home key and Power key should be only handled by System App

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https://hg.mozilla.org/integration/gaia-central/rev/975717f3d011
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Merge pull request #25719 from Cwiiis/bug1078766-hint-at-top-group

Bug 1078766 - Add a visual hint when dragging above the top group. r=crdlc,kgrandon

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https://hg.mozilla.org/integration/gaia-central/rev/8d00d2929029
Author: Chris Lord <chrislord.net@gmail.com>
Desc: Bug 1078766 - Add a visual hint when dragging above the top group. r=crdlc,kgrandon
Bumping manifests a=b2g-bump