Refactor GDM module to correspond SOLID principles

- I don't know how I will support this hell ahh code;
- Added some methods to gnome_shell_theme_builder.py;
- Added "color" property "install" method from theme_base.py.

scripts/utils/global_theme/gdm_installer.py

@@ -0,0 +1,66 @@
+from scripts.utils.global_theme.gdm_theme_prepare import GDMThemePrepare
+from scripts.utils.global_theme.ubuntu_alternatives_updater import UbuntuGDMAlternativesUpdater
+from scripts.utils.gresource.gresource import Gresource
+
+
+class GDMThemeInstaller:
+    """
+    Handles the installation of GDM themes system-wide.
+
+    This class manages:
+    - Compiling prepared theme resources into a gresource file
+    - Creating backups of original system files
+    - Installing compiled themes via the alternatives system
+    - Detecting if a theme is already installed
+    """
+    def __init__(self, gresource: Gresource, alternatives_updater: UbuntuGDMAlternativesUpdater):
+        """
+        :param gresource: Handler for gresource operations
+        :param alternatives_updater: Handler for update-alternatives operations
+        """
+        self.gresource = gresource
+        self.alternatives_updater = alternatives_updater
+
+        self._is_installed_trigger = "\n/* Marble theme */\n"
+
+    def is_installed(self) -> bool:
+        """
+        Check if the theme is installed
+        by looking for the trigger in the gresource file.
+        """
+        return self.gresource.has_trigger(self._is_installed_trigger)
+
+    def compile(self, themes: list[GDMThemePrepare], hue: int, color: str, sat: int = None):
+        """
+        Prepares themes for gresource and compiles them.
+        :param themes: themes to be compiled
+        :param hue: hue value for the theme
+        :param color: the color name. in GDM will only be shown in logger
+        :param sat: saturation value for the theme
+        """
+        self._generate_themes(themes, hue, color, sat)
+        self.gresource.compile()
+
+    def _generate_themes(self, themes: list[GDMThemePrepare], hue: int, color: str, sat: int = None):
+        """Generate theme files for further compiling by gresource"""
+        for theme_prepare in themes:
+            if theme_prepare.label is not None:
+                theme_prepare.label_theme()
+
+            theme_prepare.remove_keywords("!important")
+            theme_prepare.remove_properties("background-color", "color", "box-shadow", "border-radius")
+            theme_prepare.prepend_source_styles(self._is_installed_trigger)
+
+            theme_prepare.install(hue, color, sat, destination=self.gresource.temp_folder)
+
+    def backup(self):
+        """Backup the current gresource file."""
+        self.gresource.backup()
+
+    def install(self):
+        """
+        Install the theme globally by moving the compiled gresource file to the destination.
+        Also updates the alternatives for the gdm theme.
+        """
+        self.gresource.move()
+        self.alternatives_updater.install_and_set()