Path Expansion Autocomplete Improvements

[garrettmflynn]

This PR introduces a set of improvements to the path expansion autocomplete feature as noted by @bendichter after #609 was merged.

These include:

1. Smaller error messages across the GUIDE
2. Ability to avoid validation until user input and/or global validation of the form (which only shows requirement-based errors when necessary)
3. Infer the filesystem path type expected and constrain the selector + title accordingly
4. Change "Create" to "Submit" on the submission button
5. Provide the Source Data description (i.e. describe what file to select) when selecting an example file/folder
6. Re-render the ID inputs when the filesystem path is selected, resulting in updated validation messages

[bendichter]

looks great!