Custom Log Panel and Highlight element models

[victorviola]

• Created a custom log panel for the verification service.
• Created a context menu in the log panel
• User can now highlight or open specification for the given faulty element according to the verification service.

This PR solves issues #20 and #24.

[claudenirmf]

I have updated the code to enable the "Open Specification" action.
I have also updated the code to highlight the diagram element of the active diagram or the master view.

There is still an issue regarding the presentation of issues, there is a lot of space between items. Could you please check that out?

In addition, you don't have to crawl the model to get the elements you desire if you already have something to work with, for instance, the model element's is. Have a look at these methods:

project.getDiagramById(diagramElementId);
project.getModelElementById(modelElement);
modelElement.getDiagramElements();
diagramElement.getModelElement();

If my comment was confusing, you could have a look at how I modified openSpecDiagramElement() and highlightDiagramElement() in my last commit.

[claudenirmf]

My lastest commit seeks to help with feedback to the user so it is easier to discover this feature. It changes the following:

• Hovering over an issue changes its background color to light gray
• Both left and right clicks bring the context menu

Please verify if my changes introduce any cross-platform issues.

Btw, maybe you could solve the size issue by using JList instead of JTextArea.

[claudenirmf]

Adapted hovering selection