cpdb-backend-cups 2.0b5

In the fifth beta release for cpdb-backend-cups 2.0.0 we have removed the now unnecessary backend info file and fixed some bugs.

• Remove CPDB backend info file
  The frontend libraries now use only the D-Bus to find available backends. This makes sure that everything works also if the frontend and/or any of the backends are installed via sandboxed packaging (like Snap for example) where the components cannot read each other's file systems (PR #26).
• get_all_media(): Do not crash on custom page size range entries
  The media-col-database IPP attribute contains one entry for each valid combination of page size dimensions, margins, and in some cases also media source and media type. Entries for custom page sizes contain ranges instead of single values. get_all_media() crashed on these. Now we let the function simply skip them.
• Build system: Removed unnecessary lines in tools/Makefile.am
  Removed the TESTdir and TEST_SCRIPTS entries in tools/Makefile.am. They are not needed and let make install try to install run-tests.sh in the source directory, where it already is, causing an error.