Implement adding labels for account

This gives the user the ability to label different account (e.g. "work",
"private") and shows this label in the account switcher. Showing the
label in more places will be done in future MRs.

The label is stored in the user's account data and thus transfers
automatically to other instances of neochat

imports/NeoChat/Page/RoomListPage.qml

@@ -321,6 +321,7 @@ Kirigami.ScrollablePage {
                     Layout.fillWidth: true
                     Layout.fillHeight: true
                     text: model.connection.localUserId
+                    subtitle: model.connection.localUser.accountLabel
                 }
             }
         }

imports/NeoChat/Settings/AccountsPage.qml

@@ -151,6 +151,11 @@ Kirigami.ScrollablePage {
                 text: userEditSheet.connection ? userEditSheet.connection.localUser.displayName : ""
                 Kirigami.FormData.label: i18n("Name:")
             }
+            Controls.TextField {
+                id: accountLabel
+                text: userEditSheet.connection ? userEditSheet.connection.localUser.accountLabel : ""
+                Kirigami.FormData.label: i18n("Label:")
+            }
             Controls.TextField {
                 id: currentPassword
                 Kirigami.FormData.label: i18n("Current Password:")
@@ -179,6 +184,8 @@ Kirigami.ScrollablePage {
                             showPassiveNotification("The Avatar could not be set")
                         if(userEditSheet.connection.localUser.displayName !== name.text)
                             userEditSheet.connection.localUser.rename(name.text)
+                        if(userEditSheet.connection.localUser.accountLabel !== accountLabel.text)
+                            userEditSheet.connection.localUser.setAccountLabel(accountLabel.text)
                         if(currentPassword.text !== "" && newPassword.text !== "" && confirmPassword.text !== "") {
                             if(newPassword.text === confirmPassword.text) {
                                 Controller.changePassword(userEditSheet.connection, currentPassword.text, newPassword.text)