ADD: SocketClient/SocketServer connectors

 - By default SocketServer and SocketClient use TCP
 - SocketServer can handle several connections at a time
 - CMake variable to enable/disable feature (SOCKET_CONNECTOR)
 - Update Travis config to test SOCKET configuration
ADD: Windows support using native threads and WinSock
REF: Split threads and socket implementations
Merge branch 'feature/ADD_TcpConnector' into develop