Suggested UX tweaks for Advanced Options

[bertday]

Hello!

I've been using v1.7.5 of RPI and had two quick suggestions for how the Advanced Options dialog could perhaps be a little easier to use.

Thank you for this project and for considering these tweaks!

Add error message near the Save button

I had opened #630 because I was hitting the save button and it seemed like it wasn't doing anything, when in fact I had errors that were highlighted off-screen. (Thank you @maxnet for the tip to scroll up!)

It would be helpful if there were some text closer to the save button to let the user know why the button isn't doing anything.

Add "prefill wifi password" to options, rather than prompt

For folks who use Advanced Options often and aren't prefilling a Wi-Fi password, it may be causing some friction to have to click through this prompt every time they open the options panel:

As an alternative, would it be possible to add a button here to "fill from keychain", or something like that?