Update to new API, unify CLI, add functions for backup, autobackup and PSK handling

This pull request adds support for the APIv2 and various functions, complete with examples

change shebang to python3
update library for current unifi API
adjust parameters of other example scripts to provide the same command line interface (--debug, --no-ssl-verify, --certificate)
example script to list access points
library support to create and download backups, with example script
library support to download autobackups, with example script
library support to read and change PSK of a network by name or UUID, with example script

finish06 / pyunifi