create scancam classes

scancam_base class has only basic functionality and can be inherited by
our X-theta-z scancam or possibly by an xyz version in the future.

Existing functions were moved into the class, but there is still
substantial adaptation of the scan_action function left to complete to
make it run again.
fix device.base.do_stop_command description
create stop() and home() functs in scancam_base

Each send their command to all stages

Home waits for completion
script to test basic scancam functions
fix a bunch of hanging syntax and composition err