Time Series Visualizer

Added a first idea of a working volume time series visualizer. It came from another semi implemented solution that was already available in TVB.

- It buffers some data in advance, before it is needed. 
- The buffering is done asynchronously so we may receive  timepoint t+5 before we get t+3
- JSON parsing is done on webwokers.
- If the timepoint we want to draw has not been buffered, a blocking call is made to get it as soon as possible.

This code need some new functions from tvb-library. The pull request for that  ~~is about to come~~ is already available.

This is my first submission to TVB during Google Summer of Code 2014.