Default `application_home` is not a good general choice

[corranwebster]

The name of the application is selected by looking at the enclosing directory of the main script: https://github.com/enthought/traits/blob/66b57b7c1f2127fc070fa943773c840f5f44a9ca/traits/etsconfig/etsconfig.py#L361-L383

This is often something generic, like app, or when being run in tests is likely to be the name of the test runner (eg. unittest).

The only way to override is to completely override application_home.

Having a property that can be set for the directory name would be very useful.