[IZPACK-1195] Improve and enhance displaying of readonly UserInputPanels

This issue enhances the introduced read-only fields and panels from issue IZPACK-1120. The issue dealt exclusively for panels which are not displayed due to some not fulfilled condition and introduced the `displayHidden` attribute in the UserInputSpec.xml resource for panels and fields.

To make this more universal I'd infringe the rule to not introduce new features to 5.0 and put it to a more complete shape.

Imagine the following possibilities including those of IZPACK-1120:

**UserInputSpec.xml:**

**Introduced by IZPACK-1120:**
```xml
<panel id="panel.dbsettings.review" displayHidden="true">
...
</panel>
<panel id="panel.dbsettings.review2" >
  <field ... displayHidden="true">
  </field>
...
</panel>
```
`displayHidden="true"` (default `"false"`) introduced displaying a panel or just dedicated user input fields to be displayed read-only although they have been disabled according to a condition on the panel (install.xml, UserInputSpec.xml) or on the field (UserInputSpec.xml) .

**New attributes:**
```xml
<panel id="panel.dbsettings.review" displayHiddenCondition="SomeCondition">
...
</panel>
<panel id="panel.dbsettings.review2" >
  <field ... displayHiddenCondition="SomeCondition">
  </field>
...
</panel>
```
The `displayHiddenCondition` attribute enhances and replaces the `displayHidden` condition introduced by IZPACK-1120 and makes the related behavior dependent on another condition. Thus, the related panel or field gets displayed read-only only if a general condition on that panel or field disables it for displaying and the condition defined by `displayHiddenCondition` gets true.

```xml
<panel id="panel.dbsettings.review" readonly="true">
...
</panel>
<panel id="panel.dbsettings.review2" >
  <field ... readonly="true">
  </field>
...
</panel>
```
The `readonly` attribute is completely new and reverses the logic - `readonly="true"` means to display a complete panel or field read-only in general in case it is not disabled by a general panel or field condition.

```xml
<panel id="panel.dbsettings.review" readonlyCondition="SomeCondition">
...
</panel>
<panel id="panel.dbsettings.review2" >
  <field ... readonlyCondition="SomeCondition">
  </field>
...
</panel>
```
The new `readonlyCondition` attribute enhances and replaces the `readonly` condition and makes the related behavior dependent on another condition. Thus, the related panel or field gets displayed read-only only if it is not disabled by a general panel or field condition and the condition defined by `readonlyCondition` gets true.