Break apart client and nanostack dependencies

Move the library files used by both nanostack and client into a common
location.  This allows both client and nanostack to be built stand-alone.

The patch moves the following libraries into a common location:
-mbed-client-c
-mbed-client-randlib
-mbed-trace
-nanostack-hal-mbed-cmsis-rtos
-nanostack-libservice
-sal-stack-nanostack-eventloop

And moves the library 'coap-service' from client into nanostack.

Author: c1728p9