Add playlist creation, deletion, export and import

[laurentperez]

Hi

Like several owners, I have lost playlists due to factory resets. So I found your great project and added some useful code. I will PR on node-sonos-http-api too to reflect the new features.

• I have one test currently failing for playlist import (see npm test) because I don't know how to mock the browse response. @jishi I need your help on this one. AddUriToSavedQueue requires multiple synchronized Browse calls and I don't know how to mock them. The code is running fine, the test isn't passing because my lack of sinon knowledge.
• I bumped the version to 1.4.2 because of the future PR on node-sonos-http-api. Maybe you want to stay on 1.4.1.

[laurentperez]

for reference tracking test also fails because of https://github.com/jishi/node-sonos-discovery/issues/104

[laurentperez]

@jishi any chance you may have a look at the sinon mocked browse part ?

[jishi]

Sorry, had forgotten about this and been busy. Starting vacation today, so hopefully I will have some time for my side projects soon :)