添加API调用接口，添加读取分类，添加SpkUtils实用函数

使用了SpkSidebarTree子类实现对TreeWidget的特殊要求：不能取消选择，不能拖拽选择。

API调用接口暂时写死。API会获取

配置文件已添加但暂不使用。

gui/spksidebartree.cpp

@@ -0,0 +1,31 @@
+
+#include <QMouseEvent>
+#include "spksidebartree.h"
+
+SpkUi::SpkSidebarTree::SpkSidebarTree(QWidget *parent) :
+  QTreeWidget(parent)
+{
+
+}
+
+void SpkUi::SpkSidebarTree::mouseMoveEvent(QMouseEvent *e)
+{
+  // This is solely for forcibly  disabling the view to change selection when dragging on the view
+  // and probably the only reason why this class began its existence
+  if((e->buttons() & Qt::LeftButton))
+    setState(NoState);
+  else
+    QTreeWidget::mouseMoveEvent(e);
+}
+
+void SpkUi::SpkSidebarTree::mousePressEvent(QMouseEvent *e)
+{
+  // Prevent anything being deselected
+  if(e->modifiers().testFlag(Qt::ControlModifier) && e->buttons().testFlag(Qt::LeftButton))
+  {
+    auto i = itemAt(e->pos());
+    if(i && i->isSelected())
+      return;
+  }
+  QTreeWidget::mousePressEvent(e);
+}