Add tutorial: setting-up Bluetooth - PulseAudio

Probably needs more work, but this is a good stage to ask for comments.
On Windows the `tutorials` page did not look OK:
![tutorial_on_win7](https://cloud.githubusercontent.com/assets/8142081/5077594/11e1ed2a-6ea5-11e4-9b5d-810e3c4345cd.png)

But that could well be a jekyll on win artefact.

Q1: Yes, replacing the existing file would be good. However, see answer to Q2 for caveat.
Q2: I used the brickman test program (a desktop program built using the brickman source code) to stage the screenshots that I made - they did not actually come from a real EV3. This is why the background color is different. Also, they are scaled to 2x (without any fancy interpolation that uses anti-aliasing) so that they are easier to read. So, if you are going to go through the trouble to change the background color, you might as well scale them to 2x also.