add __ne__() function so that timeframe != timeframe works.
add __ne__() function so that timeframe != timeframe works.

nilmtk/nilmtk,AlexRobson/nilmtk,nilmtk/nilmtk,HarllanAndrye/nilmtk,mmottahedi/nilmtk,jaduimstra/nilmtk,josemao/nilmtk,pauldeng/nilmtk