Update data flow

[garrettmflynn]

This PR ensures proper data flow in the following conditions:

1. Invalid inputs into Global Metadata fields
2. Exiting and starting a new conversion after visiting the Locata Data page
3. Removing a subject / session / interface after filling out information on the Source Data (and later) page.
4. Wanting to use path expansion for one interface but not another
5. Deciding to re-run path expansion while keeping data for subjects / sessions that aren't found the second time around

Specifically for (5), I've added a new input to the top of the Locate Data page that allows users to decide to keep / clear data that already exists.

Alpha Test Issues

1. After Locate Data, extra interface source data remains in the data structure.

[garrettmflynn]

@CodyCBakerPhD Just tested this PR fully and added a few more points to the description above.

[CodyCBakerPhD]

@garrettmflynn Any idea why tests are failing?

[garrettmflynn]

Yeah just was missing a variable after the refactor. Fixed!