Add progress bar when interacting with the OntoUML sever

[tgoprince]

When requests are made to the OntoUML server (e.g. model verification, transformation to gUFO), the app does not provide any feedback to the user regarding their status or progress.

The user simply clicks a button and waits for something to happen.

Most of the time, requests are answered quickly, so this omission is not noticed. However, if they take more than a couple of seconds, the user is left wondering whether her action actually did something.

To improve the user experience, I propose that we add a progress bar on a dialog, which looks like the image below:

When the request finishes, we do not need to open a new dialog. We simple add the final message to the one that is already opened.