Improve initial active connection handling

If the last active connection is not reachable (server down, keychain problems,
token revoked, etc.), NeoChat currently fails to load at all, with the only fix
being to delete a line from the config file. This is surprisingly hard to fix with
a nice UX as long as we stick to the principle of loading the user's last active
connection automatically.

This patch thus drops that principle; instead, the user is always asked to choose
the connection to continue with.

src/qml/WelcomePage.qml

@@ -14,7 +14,12 @@ import org.kde.neochat.accounts
 FormCard.FormCardPage {
     id: root
 
+    property bool showExisting: false
+    property bool _showExisting: showExisting && module.source == root.initialStep
     property alias currentStep: module.item
+    property string initialStep: "qrc:/org/kde/neochat/qml/LoginRegister.qml"
+
+    signal connectionChosen
 
     title: i18n("Welcome")
 
@@ -42,17 +47,47 @@ FormCard.FormCardPage {
 
         FormCard.FormTextDelegate {
             id: welcomeMessage
-            text: AccountRegistry.accountCount > 0 ? i18n("Log in to a different account or create a new account.") : i18n("Welcome to NeoChat! Continue by logging in or creating a new account.")
+            text: i18n("Welcome to NeoChat")
         }
+    }
 
-        FormCard.FormDelegateSeparator {
-            above: welcomeMessage
+    FormCard.FormHeader {
+        id: existingAccountsHeader
+        title: i18nc("@title", "Continue with an existing account")
+        visible: (loadedAccounts.count > 0 || loadingAccounts.count > 0) && root._showExisting
+    }
+
+    FormCard.FormCard {
+        visible: existingAccountsHeader.visible
+        Repeater {
+            id: loadedAccounts
+            model: AccountRegistry
+            delegate: FormCard.FormButtonDelegate {
+                text: model.userId
+                onClicked: {
+                    Controller.activeConnection = model.connection
+                    root.connectionChosen()
+                }
+            }
         }
+        Repeater {
+            id: loadingAccounts
+            model: Controller.accountsLoading
+            delegate: FormCard.FormButtonDelegate {
+                text: i18nc("As in 'this account is still loading'", "%1 (loading)", modelData)
+                enabled: false
+            }
+        }
+    }
 
+    FormCard.FormHeader {
+        title: i18nc("@title", "Log in or Create a New Account")
+    }
+    FormCard.FormCard {
         Loader {
             id: module
             Layout.fillWidth: true
-            source: "qrc:/org/kde/neochat/qml/LoginRegister.qml"
+            source: root.initialStep
 
             Connections {
                 id: stepConnections