rename "Theme" selector to "Color Scheme"

Having "Color" added makes it easier to translate (i.e. Farbschema,
配色) and at least as understandable as Theme, so change it,

Suggested-by: Markus Frank <m.frank@proxmox.com>
 [ T: while Markus suggested Color Scheme, the hive-mind opted for
 this ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

src/window/ThemeEdit.js

@@ -27,14 +27,14 @@ Ext.define('Proxmox.window.ThemeEditWindow', {
 
     cookieName: 'PVEThemeCookie',
 
-    title: gettext('Theme'),
+    title: gettext('Color Theme'),
     modal: true,
     bodyPadding: 10,
     resizable: false,
     items: [
 	{
 	    xtype: 'proxmoxThemeSelector',
-	    fieldLabel: gettext('Theme'),
+	    fieldLabel: gettext('Color Theme'),
 	    bind: {
 		value: '{theme}',
 	    },