Refactoring of the Rapl backend
This is a follow-up of !104 (merged) where the code is simplified/cleaned-up using a new RaplCounter class.
The common/io.h file has been removed, in favour of using std::ifstream to read from files.
The Rapl backend is now also aware of what CPUs are used, so that in case of multi-socket systems, only the active sockets are measured.
Edited by Bram Veenboer