- Users table model renamed to UsersTableModel- causes linker conflict

with class TableModel in accomodation plugin.
- Edit record dialog is now screen centered.
- Plugin tabs in application main window are now closable.

core/defaultformhandler.cpp

@@ -1,5 +1,9 @@
 #include "defaultformhandler.h"
 
+#include <QApplication>
+#include <QDesktopWidget>
+#include <QRect>
+
 DefaultFormHandler::DefaultFormHandler()
 {
     m_dialog = new FormDialog();
@@ -14,6 +18,7 @@ void DefaultFormHandler::showForm(IForm *formWidget)
 {
     m_dialog->setForm(formWidget);
     m_dialog->setModal(true);
+    m_dialog->move(QApplication::desktop()->screen()->rect().center() - m_dialog->rect().center());
     m_dialog->show();
 }