Added support to limit number of calls per customer/profile

- added function cnxcc_set_max_channels() per customer/profile
- added function cnxcc_get_channel_count() per customer/profile
- added function cnxcc_terminate_all() to terminate calls per customer/profile
- added select @cnxcc.channels["customer/profile"].count
- added modified version of kamailio-cnxcc.cfg to refresh changes