Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/9e900ea5ab33
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Merge pull request #24791 from rjmackay/bug-1062798-settings-app-json-loading

Bug 1062798 - Replace custom JSON loaders with LazyLoader.getJSON in Settings App

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https://hg.mozilla.org/integration/gaia-central/rev/29e1ba8d5c8d
Author: Robbie Mackay <rm@robbiemackay.com>
Desc: Bug 1062798 - Replace custom JSON loaders with LazyLoader.getJSON in SettingsApp

Replace various custom JSON loaders in SettingsApp with LazyLoader.getJSON.
Refactor code to handle promises where needed, and update tests to match.
Bumping manifests a=b2g-bump