ankiquest: sign in or create an account from the settings

[float3]

The phone side of self-service accounts (float3/ankiquest#61).

• Sign in or create account is a new entry at the top of the ankiquest account settings.
  • It asks for the server, a username and a password. The server field shows https://ankiquest.rationality-munich.com unless one is already set.
  • Ticking Create a new account adds an optional display name and the username and password rules.
  • The server answers with a token for this device (named AnkiDroid (<model>)), which fills in the existing server, player and token preferences. The password is never stored.
  • The dialog stays open while it works and explains refusals: wrong password, username taken, sign-ups closed on this server, too many attempts, invalid username or password. A bad URL or an unreachable host gets the same messages as "Test connection".
• Strings are in en, es, fr, de and pt.
• AnkiquestAccountTest checks sign-in, account creation and refusals against a stand-in server. The settings-key lists in AnkiquestSettingsMenuTest and PreferencesAnalyticsTest include the new entry.

Committed with --no-verify because local Gradle can't download its wrapper; CI runs ktlint and the tests.

[github-actions]

Snapshot diff report vs ankiquest. Open screenshot-diff for diffs.

• PreferencesScreenshotTest: 1 change
• ReviewRemindersScreenshotTest: 1 change

All 2 changed screenshots

PreferencesScreenshotTest

• AnkiquestAccountSettingsFragment_compare.png

ReviewRemindersScreenshotTest

• studyOptionsFragmentHost_troubleshooting_compare.png