No way to prepend rules rather than append

[deardooley]

There is currently no way to add the new/updated rules to the head of the chain rather than the end. Append is hard-coded in the script. For users with existing catchall rules, the agave rules should optionally be inserted in front. Perhaps add -A | --append, P|--prepend, and -I|--insert [index] arguments and default to -A as the current behavior.