Automatic theme (#29)

* add "automatic" theme

set the theme and icons based on the system theme

* update the default icons based on system theme

* update pyqt to 6.5.0 to get the colorSchemeChanged callback

* rename style to theme

* remove unused svg files for default theme

* ServerInfoDialog: update feedback colors in dark mode

gotify_tray/gui/themes/dark_purple/style.qss

@@ -6,6 +6,22 @@ QPushButton:default:hover, QPushButton:checked:hover {
     background: #441b85;
 }
 
+QPushButton[state="success"] {
+    background-color: #960b7a0b;
+    color: white;
+}
+
+QPushButton[state="failed"] {
+    background-color: #8ebb2929;
+    color: white;
+}
+
+QLineEdit[state="success"] {}
+
+QLineEdit[state="failed"] {
+    border: 1px solid red;
+}
+
 QToolTip {
     color: #BFBFBF;
     background-color: #5522a8;