[feat] improve-user-feedback-on-startup

[GabrielSousa02]

What?

Added user feedback for app startup and language downloads.

• feat(l10n): add loading, startup stage and download progress strings
• feat(startup): localize loading captions and show the current startup
  stage
• test(startup): cover localized captions and startup stages
• feat(languages): show n of m progress while downloading all languages
• test(languages): cover bulk download progress reporting
• feat(android): show the logo on the native splash screen
• feat(ios): show the logo on the launch screen
• docs: document startup stages, bulk download progress and native splash
• build(ios): update auto generated iOS build files

Why?

This will improve the user experience when it comes to knowing the status of the
application setup/configuration.

How?

Added splash icons and interface components that show download status.

Testing?

New tests added and all passing.

Screenshots (optional)

Anything Else?