Set app default language as language of the user browser settings

[pavel-ilin]

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Please include the issue number the pull request fixes by replacing YOUR-ISSUE-HERE in the text below.

Fixes #657

Summary

Following @njordhov advice, default language of the app set by checking web browser settings.

Details

Add default language of the app in Translation component with using window.navigator.language.

If user browser language is not found in the backend, by default English language will be used.

Test Plan (required)

yarn start
set default language in your browser
open login page

tested in Chrome and Opera browsers.

Final Checklist

• For CoronaTracker, did you bump the version in package.json?
  • Update the second decimal for a major change
  • Update the third decimal for a minor change
  • Numbers can go past 9, e.g. 1.0.9 => 1.0.10
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• Did you add any new tests as necessary?
• Is your PR rebased off the most current master?
• Have you squashed all commits? (can be done at merge)
• Did you use yarn not npm? (important!)
• Did you use Material-UI wherever possible?
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