added content description to navigation buttons and removed unused functions (#307)

.../coronawarnapp/ui/information/InformationAboutFragment.kt

...oronawarnapp/ui/information/InformationContactFragment.kt

...e/rki/coronawarnapp/ui/information/InformationFragment.kt

.../coronawarnapp/ui/information/InformationLegalFragment.kt

...oronawarnapp/ui/information/InformationPrivacyFragment.kt

...onawarnapp/ui/information/InformationTechnicalFragment.kt

.../coronawarnapp/ui/information/InformationTermsFragment.kt

...java/de/rki/coronawarnapp/ui/settings/SettingsFragment.kt

...va/de/rki/coronawarnapp/util/formatter/FormatterHelper.kt

Corona-Warn-App/src/main/res/layout/fragment_main.xml

...src/main/res/layout/fragment_onboarding_notifications.xml

...n-App/src/main/res/layout/fragment_onboarding_privacy.xml

...Warn-App/src/main/res/layout/fragment_onboarding_test.xml

...n-App/src/main/res/layout/fragment_onboarding_tracing.xml

.../src/main/res/layout/fragment_submission_qr_code_scan.xml

Corona-Warn-App/src/main/res/layout/include_button_icon.xml

Corona-Warn-App/src/main/res/layout/include_header.xml

...c/main/res/layout/include_submission_status_card_done.xml

...in/res/layout/include_submission_status_card_positive.xml

Corona-Warn-App/src/main/res/values/strings.xml