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

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https://hg.mozilla.org/integration/gaia-central/rev/171a802a78fd
Author: Olle Klang <olle.klang@sonymobile.com>
Desc: Bug 1069840 - Update apps links to fetch shared style from default theme r=vingtetun

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https://hg.mozilla.org/integration/gaia-central/rev/9f6bb27f0bb2
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Revert "Update links to fetch gaia-theme from default theme."

This reverts commit 2896d5ff8e3b531c3d26b216102ebe55f0cfb5d0.

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https://hg.mozilla.org/integration/gaia-central/rev/8bcf65a3bdfd
Author: Marshall Culpepper <marshall.law@gmail.com>
Desc: Merge pull request #24844 from marshall/bug1070858_appUsageOnline

Bug 1070858: [AppUsageMetrics] Track online status through navigator.onLine

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https://hg.mozilla.org/integration/gaia-central/rev/a4cf07e8db23
Author: Marshall Culpepper <marshall@mozilla.com>
Desc: Bug 1070858: [AppUsageMetrics] Track online status through navigator.onLine r=djf
Bumping manifests a=b2g-bump