UI: Add Grid Mode to Scenes Widget

Adds an option to the right click menu in the scenes widget to switch
modes. When in regular list mode, it'll let you select grid mode, and in
grid mode, it'll let you select list mode. Grid mode changes the scenes
widget to have a grid of buttons for scenes rather than a list, much
like XSplit.

UI/data/themes/Acri.qss

@@ -1022,3 +1022,25 @@ OBSBasic {
     qproperty-sceneIcon: url(./Dark/sources/scene.svg);
     qproperty-defaultIcon: url(./Dark/sources/default.svg);
 }
+
+/* Scene Tree */
+
+SceneTree#scenes {
+    qproperty-gridItemWidth: 180;
+    qproperty-gridItemHeight: 35;
+}
+
+*[gridMode="true"] SceneTree#scenes {
+	border-bottom: none;
+}
+
+*[gridMode="false"] SceneTree#scenes {
+	border-bottom: 2px solid #2f2f2f;
+}
+
+*[gridMode="true"] SceneTree::item {
+    padding: 4px;
+    padding-left: 10px;
+    padding-right: 10px;
+    margin: 0px;
+}

UI/data/themes/Dark.qss

@@ -12,6 +12,7 @@
 /*   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the            */
 /*   GNU General Public License for more details.                             */
 /*                                                                            */
+/*                                                                            */
 /*   You should have received a copy of the GNU General Public License        */
 /*   along with this program.  If not, see <http://www.gnu.org/licenses/>.    */
 /******************************************************************************/
@@ -774,3 +775,37 @@ OBSBasic {
     qproperty-sceneIcon: url(./Dark/sources/scene.svg);
     qproperty-defaultIcon: url(./Dark/sources/default.svg);
 }
+
+/* Scene Tree */
+
+SceneTree {
+    qproperty-gridItemWidth: 150;
+	qproperty-gridItemHeight: 27;
+}
+
+*[gridMode="true"] SceneTree::item {
+    color: rgb(225,224,225); /* veryLight */
+    background-color: rgb(76,76,76);
+    border: none;
+    border-radius: 3px;
+    padding: 4px;
+	padding-left: 10px;
+	padding-right: 10px;
+	margin: 1px;
+}
+
+*[gridMode="true"] SceneTree::item:selected {
+    background-color: rgb(122,121,122); /* light */
+}
+
+*[gridMode="true"] SceneTree::item:hover {
+    background-color: rgb(122,121,122); /* light */
+}
+
+*[gridMode="true"] SceneTree::item:pressed {
+    background-color: rgb(31,30,31); /* veryDark */
+}
+
+*[gridMode="true"] SceneTree::item:checked {
+    background-color: rgb(122,121,122); /* light */
+}

UI/data/themes/Rachni.qss

@@ -1365,3 +1365,10 @@ OBSBasic {
     qproperty-sceneIcon: url(./Dark/sources/scene.svg);
     qproperty-defaultIcon: url(./Dark/sources/default.svg);
 }
+
+/* Scene Tree */
+
+SceneTree#scenes {
+    qproperty-gridItemWidth: 150;
+    qproperty-gridItemHeight: 30;
+}

UI/data/themes/System.qss

@@ -233,3 +233,10 @@ QListWidget::item,
 SourceTree::item {
 	height: 24px;
 }
+
+/* Scene Tree */
+
+SceneTree {
+    qproperty-gridItemWidth: 150;
+	qproperty-gridItemHeight: 24;
+}