Internationalization (German) of the mobile app. (#246)

* Add i18n framework to mobile app and write simple translation generator

* Replace all texts in login_form with i18n keys

* Localization of sharing section

* Localization of asset viewer section

* Use JSON as base translation format

* Add check for missing/unused translation keys

* Add localizely

* Remove i18n directory in favour of localizely

* Backup Translation

* More translations

* Translate home page

* Translation of search page

* Translate new server version announcement

* Reformat code

* Fix typo in german translation

* Update englisch translations

* Change translation keys to match dart filenames

* Add /api to translated endpoint_urls

* Update localizely.yml

* Add languages to ios plist

* Remove unused keys

* Added script to check outdated key in other translations

* Add download key to localizely.yml

Co-authored-by: Alex <alex.tran1502@gmail.com>

mobile/pubspec.yaml

@@ -40,6 +40,7 @@ dependencies:
   url_launcher: ^6.1.3
   http: 0.13.4
   cancellation_token_http: ^1.1.0
+  easy_localization: ^3.0.1
 
   path: ^1.8.1
   path_provider: ^2.0.11
@@ -59,6 +60,7 @@ flutter:
   uses-material-design: true
   assets:
     - assets/
+    - assets/i18n/
   fonts:
     - family: WorkSans
       fonts: