This PR is an alternative to #1429. Instead of using click-specific decorators for every command, it simply installs a `sys.excepthandler` to deal properly with exceptions. Advantages over #1429: - Simpler - Covers the store CLI with no additional work - Covers future CLI additions automatically, nothing special needed Disadvantages compared to #1429: - Can no longer unit test CLI exit codes since the CLI is run within the same python process, the test catches the exception, and `excepthook` is never called. Integrations tests are needed instead. - Global behavior can cause unexpected things to happen (i.e. the simple fact that some exceptions are masked by a global handler may be unexpected a year down the road when we add a new command)