ui: Added history of last active symbols to UI and menu (issue 151)

* holding down back or forward button shows list of current back-forward stack
* added narrow button between back and forward to show the list
* added History menu
* moved back and forward actions to History menu
* show chronological list of recently active symbols in History menu

bug id = 151

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bin/app/data/gui/history_list/history_list.css

@@ -0,0 +1,19 @@
+QListWidget::item {
+	border-bottom: 1px solid <color:search/popup/background>;
+}
+
+#history_list {
+	background: <color:search/popup/background>;
+}
+
+#history_item, #history_item_current {
+	color: <color:search/popup/text>;
+	font-family: "<setting:font_name>";
+	font-size: <setting:font_size>px;
+	padding-left: 20px;
+	padding-top: 1px;
+}
+
+#history_item_current {
+	font-weight: bold;
+}

bin/app/data/gui/undoredo_view/undoredo_view.css

@@ -5,7 +5,6 @@
 QPushButton {
 	background: <color:search/button/normal>;
 	border: none;
-	background-position: 15px 5px;
 	height: 30px;
 	width: 30px;
 }
@@ -13,7 +12,6 @@ QPushButton {
 #undo_button {
 	border-bottom-left-radius: 12px;
 	border-top-left-radius: 12px;
-	margin-right: 2px;
 }
 
 #redo_button {
@@ -21,6 +19,12 @@ QPushButton {
 	border-top-right-radius: 12px;
 }
 
+#history_button {
+	width: 14px;
+	margin-left: 2px;
+	margin-right: 2px;
+}
+
 QPushButton:disabled {
 	background: <color:search/button/disabled>;
 }