change relational imports for Python 3 compatibility

[Sir-Nightmare]

I had problems with launching hub with Python 3.5, so I changed imports according to python docs. https://docs.python.org/3/tutorial/modules.html#intra-package-references

[databobek]

@boakley this code is necessary, because in this scenario, py3 is looking for kwdb in PYTHONPATH while it is a local file. Adding the code proposed by @Sir-Nightmare tells py3: "it's here, don't look anywhere else". This is the reason for import kwdb crash.