Uniform Grpc signaling

This release introduces an Grpc based signaling which can be used by communication policies.
Currently it is only used by the ZeroMq communication policy, but will also be used by the
upcoming Asio communication policy.

The following list summarises the changes:

• Grpc based signaling
• Renamed signaling server to signaling
• Add communication policy probe method
• Provide concepts definitions
• Implement serialization policy interface
• Provide benchmark target
• Update documentation

New Communication Policy ZeroMQ

This release fixes all issues of the ZeroMQ milestone and provides the new communication policy ZeroMQ which enables for communication based on tcp, udp and inter process communication.

The following list summarises the changes:

• New ZeroMQ communication policy
• Divide communication policy into core and collective api
• Provide base class for communication policy based on CRTP
• Introduction of edge and vertex communication interface
• Extensive testing by target test
• New mappings and patterns
• Updated documentation

The GrayBat is ready to explore the world

This is the first release fixing all issues mentioned for
First Release Milestone.

The release provides:

• Full documentation
• Unit tests (For checking further communication libraries)
• Predefined communication patterns and vertex mappings
• Graphs based on Boost Graph Library
• Communication based on Boost MPI
• Game of life example