[UML_VIEW] Bug-fixing of the UML view

[svlad-90]

The following bug-fixes should be applied as the result of this task:

• Ignore duplicated UEV, URS, URT elements. Apply "first win" strategy in case of found duplicates
• Notify the user about the duplicated UEV, URS, URT elements
• Wrap UCL and US into the "" to allow usage of the wider set of characters
• Fix debug output issue - previous successfully created diagram was printed in debug console instead of the one which contains an error
• Render plantuml error image in the plugin