[Usability] Inform user about error, progress, and task completion

[flantony]

We need a proper mechanism to inform the user about errors that have occured during certain tasks. For example if the compiler call failed due to a wrong path, the user currently gets the impression the call never happened. Instead we need feedback that states the nature of the problem and helps to solve it.

Possible options: Pop-up-dialog, Error-View, ...

[tkutz]

What about using console view for that? We could also log on different levels, e.g. LogLevel.Info just prints that solc was invoked and how many issues were reported, while LogLevel.Fine would print the exact json inputs/outputs.