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

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https://hg.mozilla.org/integration/gaia-central/rev/bae982d96783
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #17376 from timdream/system2-screenshot-land

Bug 971546 - [System2] Instantiable Screenshot, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/b85e1473bc01
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Revert "Revert "Bug 971546 - [System2] Instantiable Screenshot" for possibly breaking gaia-ui tests on TBPL"

This reverts commit 60e9eb1aa68a27fa21e75264e52409aa5a2b4cc4.

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https://hg.mozilla.org/integration/gaia-central/rev/3d1104c7bb1f
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #17475 from timdream/system2-visibility-manager

Bug 971577 - [System] Make visibility manager instantiable +shepherd, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/484d7196ef1d
Author: Rex Lee <rexboy@mozilla.com>
Desc: Bug 971577 - [System] Make visibility manager instantiable
Bumping manifests a=b2g-bump