improve the error indication

[akiou]

In the current implementation, Kanon shows which part of the program has an error below the editor pane only by textual if the user program has an error. We have to improve the error indication to more user-friendly.

[Iodine98]

I think you solved the problem, by adding the error and warning icons and a tooltip when hovering in the editor:

* I wrote wrong syntax on purpose to show the example above