Change port’s Label to a CheckBox

For host, database name, and options i can leave them blank to use the
default value, but for the port i can’t with a SpinBox, since it _must_
have a value.

Qt’s driver uses -1 to mean “default port”, but i can not use the same
approach with the user interface, because there is no port -1, and makes
no sense to allow that value, specially since i then i have to allow 0
as well, which is a reserved port.

I also can not leave the SpinBox with PostgreSQL’s default port, 5432,
because that is slightly different than telling libpq to use the
“default”: if someone uses a ‘service=’ option, it would use the port in
the SpinBox rather than the one in ‘pg_service.conf’, if any.

My solution is to use a checkbox to tell the application “i wan to use a
port number”, and (will) only pass the port number if it is checked.  On
the other hand, now i do not have a keyboard shortcut to focus on the
port number field.

src/LoginPage.qml

@@ -67,17 +67,27 @@ Page {
                     onAccepted: loginAction.trigger()
                 }
 
-                MnemonicLabel {
+                CheckBox {
+                    id: port
+
                     Layout.alignment: Qt.AlignRight
-                    buddy: port
-                    mnemonic: qsTr("Por&t:")
+                    Mnemonic.label: qsTr("Por&t:")
+                    text: Mnemonic.richTextLabel
+
+                    Shortcut {
+                        sequence: port.Mnemonic.sequence
+
+                        onActivated: port.click()
+                    }
                 }
 
                 SpinBox {
-                    id: port
+                    id: portNumber
 
+                    Accessible.name: qsTr("Port number")
                     Layout.fillWidth: true
                     editable: true
+                    enabled: port.checked
                     from: 1
                     to: 65535
                 }