Script identifiers should use normalized file paths

[ctrueden]

Script identifiers are currently formed as script: plus the path to the script. But no normalization is done, so on Windows, such identifiers will contain backslashes. E.g. script:C:\Fiji\plugins\Scripts\Plugins\BigStitcher\Custom Scripts\BigStitcher_Flip_Axes.groovy. We should normalize the path the same way Java does in other places: by replacing backslashes with forward slashes. This avoids issues with the backslash character needing to be escaped.

Reported by @lacan here.