applications-panel: Set minimum width and height for the "Required Access" and "Links & File Associations" dialogs

"Built-in Permissions" dialog appears with a really small size, making elements almost invisible. Plus, It can be shrunken to an even smaller size.

"Link & File Associations" dialog can also be shrunken to a really small size, making elements almost invisible too:

This MR sets a minimum width and height for both dialogs.

Before	After

I used the same width and height from the "Link & File Associations" dialog.

Does this look ok, @bertob? I mentioned you because recently you suggested a size change for the Epiphany preferences dialog.

Fixes: #1826 (closed)