avoid master/slave terminology

[gen2thomas]

avoid master/slave terminology

[gen2thomas]

Additionally:

• same as above for usages in I2C, use "controller/target", following the NXP decision, i2c-bus.org
• substitute wrong github-paths https://github.com/hybridgroup/gobot/<blob/tree>/master to the "release" path
• master.go with manager.go, same for related types
• search for remaining occurrences of "master" and replace e.g. by one of the following names:
  controller, default, director, host, initiator, leader, manager, primary, principal, root
• search for remaining occurrences of "slave" and replace e.g. by one of the following names:
  agent, client, device, performer, peripheral, replica, responder, satellite, secondary, subordinate, worker