software/theia: Fix exporter.exclude logic

1. Rework exporter.exclude logic, with the following goals in mind:

   • exporter.exclude may contain absolute paths for convenience (so that SRs may write e.g. $${directory:logs})
   • exporter.exclude lists paths and patterns of paths that must not be transferred to theia1, but that should be preserved in theia1 if they already exist there.
   • __buildout_installed__ paths listed in .installed*.cfg should not be transferred to theia1, and should be deleted if they already exist in theia1. There is no need to parse .installed*.cfg in theia1, as any paths not included in the transfer and not matched in exporter.exclude will be deleted by default.

2. Change backup signature logic to support non-ascii file and folder names by ensuring filepaths are represented on a single line even when they contain non-printable, newline or non-ascii characters, or even when their encoding it not valid utf-8.