Add dialog for changing alias; improve dialog buttons in general

src/main/kotlin/androidx/compose/material/DialogButton.kt

...org/briarproject/briar/desktop/contact/ContactDropDown.kt

...ject/briar/desktop/contact/add/remote/AddContactDialog.kt

...project/briar/desktop/conversation/ConversationDialogs.kt

...rproject/briar/desktop/conversation/ConversationHeader.kt

...briar/desktop/conversation/ConversationRequestItemView.kt

...rproject/briar/desktop/conversation/ConversationScreen.kt

...oject/briar/desktop/conversation/ConversationViewModel.kt

...otlin/org/briarproject/briar/desktop/login/LoginScreen.kt

src/main/resources/strings/BriarDesktop.properties