contrib: rename udev rules for correct rule ordering on systemd systems

The "uaccess" tag has to be added before the "seat" rule is evaluated.
The upstream default for the seat rule is "71-seat.rules", so use
60-libsigrok.rules for appropriate lexicographical sorting.

Also use a dash instead of underscore, the latter is commonly used as a
replacement character of unsafe characters in autogenerated identifiers.

This fixes bug #1059.