Add RPC convenience classes

- AsyncServiceClient when you don't want to block for a #$%!@!! service call
- EasyActionServer when you want to implement a RPC call in 3 lines
Small pep8 adjustment
pal_common: add @configurable class decorator

This helps setting configuration parameters to objects and
default values. The doc is in the code.
pal_hci: add a REEM ear LED client
Add corrections following pull request comments
Merge pull request #1 from pal-robotics/additions

A few additions