Fixing examples by initializing with streams

[OrganicIrradiation]

Neither the show_cv2 nor the show_matplotlib examples were working for me with an Intel RealSense R200 without initializing the streams.

[toinsson]

hello, thanks for the contribution.

I am a bit surprised about not having the streams initialised.
At:

pyrealsense/pyrealsense/core.py

Line 165 in 1b32791

if streams is None:

and later:

pyrealsense/pyrealsense/core.py

Line 196 in 1b32791

for s in streams:

The default streams are enabled. Do you know what is going on with R200?

Related to issue #54, thanks for the new streams. Might be valuable to put them in stream.py.

[OrganicIrradiation]

Hmm, I'll check it out more in depth this upcoming week and get back to you about the initialization of the default streams. Let's hold off on the PR until then.