Bumping gaia.json for 7 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/ec735620fcff
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #17263 from gasolin/bubble-merge225

cherry-pick Bubble-tea

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https://hg.mozilla.org/integration/gaia-central/rev/94c37dafac4e
Author: EragonJ <eragonj@eragonj.me>
Desc: Bug 974828 - [Settings][dsds] Outgoing data confirmation is wrong

- update test
- change the way about how we show confirm window

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https://hg.mozilla.org/integration/gaia-central/rev/cda9fc54ec17
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 970028 - Nicer activity opener animation

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https://hg.mozilla.org/integration/gaia-central/rev/1ef05f8d675f
Author: Cédric de Saint Martin <cedric.dsm@tiolive.com>
Desc: Bug 971556 - [System2] Instantiable SourceView.

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https://hg.mozilla.org/integration/gaia-central/rev/671cfdfc031b
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 961800 - Implement Child Window Factory

Conflicts:
	apps/system/js/app_transition_controller.js
	apps/system/js/app_window.js
	apps/system/js/app_window_manager.js
	apps/system/js/cards_view.js
	apps/system/style/window.css

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https://hg.mozilla.org/integration/gaia-central/rev/79679041e3f0
Author: Rex Lee <rexboy@mozilla.com>
Desc: Bug 971577 - [System] Make visibility manager instantiable

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https://hg.mozilla.org/integration/gaia-central/rev/9573ca6d00fa
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 971546 - [System2] Instantiable Screenshot
Bumping manifests a=b2g-bump