Add homeserver URL field to login screen

TODO.md

@@ -58,11 +58,11 @@
   - Prevent others from having a too similar hue as us, or our own accounts
     from sharing a too similar hue
   - Combine events so they take less space
-    - After combining is implemented, no need to hide our own profile changes.
+    - After combining is implemented, no need to hide profile changes anymore.
   - Replies
   - Messages editing
   - Code highlighting
-  - Support GIF avatars
+  - Support GIF avatars and images
   - Adapt shortcuts flicking speed to font size and DPI
 
   - EditAccount page:

src/python/backend.py

@@ -49,7 +49,7 @@ class Backend:
         user:       str,
         password:   str,
         device_id:  Optional[str] = None,
-        homeserver: str = "https://matrix.org",
+        homeserver: str           = "https://matrix.org",
     ) -> Tuple[bool, str]:
 
         client = MatrixClient(

src/qml/Pages/SignIn.qml

@@ -4,7 +4,8 @@ import "../Base"
 
 HPage {
     property string loginWith: "username"
-    readonly property bool canLogin: idField.text && passwordField.text
+    readonly property bool canLogin:
+        serverField.text && idField.text && passwordField.text
 
     onFocusChanged: idField.forceActiveFocus()
 
@@ -27,7 +28,10 @@ HPage {
 
             login: button => {
                 button.loading = true
-                let args = [idField.text, passwordField.text]
+                let args = [
+                    idField.text, passwordField.text,
+                    undefined, serverField.text,
+                ]
 
                 py.callCoro("login_client", args, ([success, data]) => {
                     if (! success) {
@@ -74,6 +78,14 @@ HPage {
             }
         }
 
+        HTextField {
+            id: serverField
+            placeholderText: qsTr("Homeserver URL")
+            text: "https://matrix.org"
+
+            Layout.fillWidth: true
+        }
+
         HTextField {
             id: idField
             placeholderText: qsTr(