Bus single slave view not passed slave index

After changing from init from bus to init from config file, the slave now does not have a valid slave index at creation. The bus single slave view is a dependency of a slave and thus needs to be created before the slave and way before the bus is even queried or initialised.

Two options:

1. remove slave index convenience and always pass slave index in calls on bus single slave view
2. find another API to initialize the slave index; maybe a specific entry point after going into pre-op when slave id is known and slaves on EtherCAT bus were read