Reformat and define exports in cmdlib/__init__.py

cmdlib/__init__.py now simply defines the interface of the cmdlib module
by importing all classes which should be visible to clients.

Also don't ignore C0302 (Too many lines in module) any more.

Signed-off-by: Thomas Thrainer <thomasth@google.com>
Reviewed-by: Bernardo Dal Seno <bdalseno@google.com>