New dependency pyotb

I can understand if you want to keep minimal dependencies, but pyotb is quite stable now and soon we'll push 2.0.
First, it can divide code length by 3 or 4, by removing the SetParameter verbose stuff, and simplify the numpy exports and pixel type management.
It also adds a python logger layer that is missing in the bare otbApplication.py (we only see the C++ stuff from otb subprocess), and is more user friendly in regard of the import otbApplication => ImportError nightmare.

But what is really nice that it allow us to easily subclass OTB applications.
Rémi did this in scenes and it's quite powerful.
By the way scenes is also something we could use in the future to manage data (remote) sources.