Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/0838151416d2
Author: Marshall Culpepper <marshall.law@gmail.com>
Desc: Merge pull request #21215 from marshall/bug982663_metricsAppUsage

Bug 982663: Collect and report app usage data

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https://hg.mozilla.org/integration/gaia-central/rev/3f5f9ae97be0
Author: Marshall Culpepper <marshall@mozilla.com>
Desc: Bug 982663: Part 2 - Integration tests and follow up for App Usage metrics. r=etienne

* Use ftu.pingURL as the default base URL for app usage metrics
* Added tests for app usage default values
* Use manifestURL instead of origin to track unique apps

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https://hg.mozilla.org/integration/gaia-central/rev/dba5b4a3f2ac
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 982663: Part 1 - Collect and report app usage data. r=etienne

* record app installation and uninstallation
* send a unique device id with each report
* report deviceinfo, language and screen data, and make telemetry parameters
  configurable through settings
* Refactor to match system app module structure
* Unit tests and bug fixes
* Change strings in Settings and FTU apps to mention app usage data collection
* Address review comments
* Fix failing bootstrap tests
Bumping manifests a=b2g-bump