widgets: file save dialog: Add overwrite checks
widgets: file save dialog: Add overwrite checks

Now the dialog shows "Overwrite $name?" popup when file already exists
and also if there is a directory with the name we show a warning.

TODO: Set the input field alert when name matches directory?

Signed-off-by: Cyril Hrubis <b1e90efd3b808b8e0bcf2a9a55fd8b9a779bfd81@ucw.cz>

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