Improve error message when importing an existing app in the App Studio
When importing an existing app and the manifest file is not correct, the error displayed is "Import package failed. Make sure the package is correct.". The error is not very helpful and could be more specific. Is it the manifest file that is incorrect? is the manifest file missing? Are other files missing? Also, what could be a suggested work around? e.g. check the format of the manifest file with the schema checker or similar. Anything is better than "Make sure the package is correct".