Fixed build issues

Fixed build with cmake when including limereport as a submodule with add_subdirectory(...)
Removed unnecessary checks of ENABLE DIALOG DESIGNER in CMakeLists.txt
Fixed Qt 5.15.16 incompatibility
Added missing LIMEREPORT_EXPORT
Fixed warnings

limereport/objectinspector/editors/lrcomboboxeditor.h

@@ -33,6 +33,7 @@
 #include <QComboBox>
 #include <QWidget>
 //#include <QPushButton>
+#include "lrglobal.h"
 
 class QToolButton;
 
@@ -58,7 +59,7 @@ private:
     bool m_popup;
 };
 
-class ComboBoxEditor: public QWidget {
+class LIMEREPORT_EXPORT ComboBoxEditor: public QWidget {
     Q_OBJECT
 public:
     // explicit ComboBoxEditor(QWidget *parent = 0);

limereport/objectinspector/lrobjectpropitem.h

@@ -42,7 +42,7 @@
 
 namespace LimeReport {
 
-class ObjectPropItem: public QObject {
+class LIMEREPORT_EXPORT ObjectPropItem: public QObject {
     Q_OBJECT
 
 public: