Update directory selector widget

The directoryInput.R helper widget has been updated upstream since the moment it was included in the EcoValApp (w/ authored upstream extensions); the improvements regards in particular Windows directory selector (w/ batch inlined now in R code):

## uses a powershell script rather than the bat version, gives a nicer interface
## and allows setting of the default directory and the caption

The default/selected directory setting was resolved locally by PowerShell injection into the batch script. In some Windows environments, for security reasons, it's not to allowed to run "hybrid" PowerShell and batch scripts, hence, pure PowerShell script is better.

Note: directory_input_binding.js--the JS part of the widget that we also include--at the moment of writing (22 Mar 2022) has not been changed upstream; do double-check.