Move UI classes into packages

mailbox-android/src/main/AndroidManifest.xml

...va/org/briarproject/mailbox/android/MailboxPreferences.kt

...n/java/org/briarproject/mailbox/android/MailboxService.kt

.../java/org/briarproject/mailbox/android/ui/MainActivity.kt

...g/briarproject/mailbox/android/ui/setup/QrCodeFragment.kt

...iarproject/mailbox/android/ui/setup/QrCodeLinkFragment.kt

...project/mailbox/android/ui/setup/SetupCompleteFragment.kt

...g/briarproject/mailbox/android/ui/startup/InitFragment.kt

...mailbox/android/ui/startup/OnboardingContainerFragment.kt

...rproject/mailbox/android/ui/startup/OnboardingFragment.kt

...ject/mailbox/android/ui/startup/StartupFailureActivity.kt

...riarproject/mailbox/android/ui/startup/StartupFragment.kt

...iarproject/mailbox/android/ui/status/ClockSkewFragment.kt

...iarproject/mailbox/android/ui/status/NoNetworkFragment.kt

.../briarproject/mailbox/android/ui/status/StatusFragment.kt

...riarproject/mailbox/android/ui/status/StoppingFragment.kt

...arproject/mailbox/android/ui/wipe/WipeCompleteActivity.kt

...arproject/mailbox/android/ui/wipe/WipeCompleteFragment.kt

...rg/briarproject/mailbox/android/ui/wipe/WipingFragment.kt

...ox-android/src/main/res/layout/activity_wipe_complete.xml