Improve error handling

[clochix]

When an exception is raised, we catch it and send it to the server. But we didn't provide any feedback to the user. The exception often means that the user attempted an action that failed, and he didn't get any feedback. This is really frustrating. So, when an exception is thrown, we should notify the user (and maybe suggest to use the contact form to explain how to reproduce the issue ? When we see error stack on server side, we often miss context.)