Disable file migration for 0.7.0

This pull request addresses the following defect:

[MAGN-2381 Disable auto migration and warn users if they are trying to open older version file.](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-2381)

It also implements a new ```GenericTaskDialog``` for use in displaying the error message. In the near future, ```CrashPrompt``` will be replaced by this dialog.