- 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/formdialog.ui

@@ -2,6 +2,9 @@
 <ui version="4.0">
  <class>FormDialog</class>
  <widget class="QDialog" name="FormDialog">
+  <property name="windowModality">
+   <enum>Qt::ApplicationModal</enum>
+  </property>
   <property name="geometry">
    <rect>
     <x>0</x>
@@ -11,7 +14,7 @@
    </rect>
   </property>
   <property name="windowTitle">
-   <string>Dialog</string>
+   <string>Edit record</string>
   </property>
   <layout class="QVBoxLayout" name="verticalLayout_2">
    <property name="leftMargin">