rename images: preserve extension with option to change + option to willingly move files.

[anoderay]

Supersedes #712 and #713

Enhances the existing rename_images.lua:

• Preview button for renaming pattern
• Ensure we always rename with a valid extension with the option to change to a custom extension (because darktable always expects a valid extension as demonstrated by Renaming without file extension causes crash darktable#21684)
• Various sanitizations of special characters etc.: forbidden filesystem characters (<>:"|?* + control characters) always replaced with -
• Give the option to move files. The current behaviour when using / or \ in the renaming pattern was confusing and IMHO produced unintuitive results.
  • when allow moving files is "off" \ and / resolve to -.
  • When allow moving files is "on" a relative path from the current location of the image is constructed.
  • Absolute paths are not supported but IMHO this is necessary to safeguard against moving files to the filesystem root etc.

@wpferguson I`d be happy if you could take a look :-).

Co-Created with Claude Sonnet 5.