Added a camera permission check before the scanner route is opened

[fkloes]

Description

This ticket is about to "protect" the scanner route with a camera permission check. So when the route is opened, and the permissions are not granted yet, we'll present a dialog to the user where he can directly grant permissions - if possible -, or first navigate to the settings.

Type of change

• Bug Fix 🐛 (non-breaking change which fixes an issue)
• New Feature 🚀 (non-breaking change which adds functionality)
• Breaking Change 💥 (fix or feature that would cause existing functionality to not work as expected)
• Polish 💅 (Just some cleanups)
• Docs 📝 (Changes in the documentations)
• Internal 🏠 Only relates to internal processes.

How to test it

Open a fresh installed app, or revoke the camera permissions for one that is already installed. Try to navigate to the scanner page.

To test the full feature, you'll need an app, that supports the new scanner. But since the permission commands exist since Lib 18.0, you could also add a link to the scanner route with a HTML widget.

[coveralls]

Pull Request Test Coverage Report for Build 2298

• 28 of 50 (56.0%) changed or added relevant lines in 5 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.05%) to 50.869%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
themes/theme-gmd/pages/subscriptions.js	0	11	0.0%
themes/theme-ios11/pages/subscriptions.js	0	11	0.0%

Files with Coverage Reduction	New Missed Lines	%
themes/theme-gmd/pages/subscriptions.js	1	0.0%
themes/theme-ios11/pages/subscriptions.js	1	0.0%

Totals
Change from base Build 2296:	0.05%
Covered Lines:	5716
Relevant Lines:	10636

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💛 - Coveralls