pbr: update to 1.1.4-r15

* delete obsolete files/etc/init.d/pbr.init
* add files/etc/uci-defaults/91-pbr-iptables to help update from older OpenWrt
* add files/etc/uci-defaults/91-pbr-nft to help update from older OpenWrt
* update files/etc/uci-defaults/91-pbr-netifd to only add tables to supported ifaces
* re-organize variants in the Makefile so that they hopefull work this time
* update prerm for all variants for better user experience
* update the -netifd prerm to remove leftofver entries from network and rt_tables file

In the init script:
* add decorations for netifd-interfaces related operations (blue ticks)
* add rtTablesFile variables instead of hard-coding the rt_tables file
* add function to check if the table is netifd-derived
* add error messages/hints for failed interface setup and failed WAN discovery
* make cleanup_rt_tables the netifd-compatible
* streamline interface_process function with a clearer case statement
* rename the interface_process `pre-init` option to `pre_init` to conform to the other
  functions options naming style

Signed-off-by: Stan Grishin <stangri@melmac.ca>