[birt-dev] Checkin: fix bugs 226438:Insert image dialog enhancement

["Xiong Zhang" <xiong.zhang@xxxxxxxxxxx>]

- Summary:
Insert image dialog enhancement

- Bugzilla Bug (s) Resolved:
226438

- Description:
1.Add FocusListener for text control to preview image after it loses focus.
2.Update error message when file name is duplicate.

- Tests Description :
Manual test

- Files Edited:

/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/nls/messages.properties
/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/ImageBuilder.java

- Files Added:

- Files Deleted:

- Notes to Build Team:

- Notes to Developers:

- Notes to QA:

- Notes to Documentation: