Better handle errors

[SebastienTouze]

I thought about something, currently whe we get an error it is handled locally, eg. if the use tries to deletes a file which do not exist a QMessageBox explaining the error is shown. The same is done with every error, maybe a common function for that could be useful like for the Maccaw::DEBUG function ? We can make very easily a Macaw::ShowError, do you think this is appropriate @ochurlaud ?

[ochurlaud]

Yes it can be but not for know... we first need a first release

[ochurlaud]

Use signals with error type (WARNING, DEBUG, INFO) + Message that triggers a slot in Application