filepicker option to default to CWD

[RyanDraves]

While using the filepicker bubble, I was unable to make a directory selection default to the CWD, which felt like an awkward workflow for my use case. I have this feature implemented with accompanying tests, where a setter is used before Init is called to get the relevant model state set correctly.

Somewhat related FileSelected has no references and is never updated. I added logic to update it the filepicker is navigated and wrote some tests for that as well.