New api, to easily use VisTrails in other applications

This adds an easy-to-use API, that hides the internals and exposes wrappers.

* [X] VisTrails initialization
 * Don't load packages at startup
 * Fixes argv handling for IPython
 * Fixes logging
* [X] Loading pipelines and vistrails
* [X] Package and namespace wrapper
* [X] Execution
 * [ ] Sending custom input to pipeline
 * [ ] Getting execution output
 * [ ] IPython integration (rich-text)
* [ ] "Output modes"
* Pipeline modification, can be done in a future iteration

Current status: [notebook](http://nbviewer.ipython.org/gist/remram44/2a67e6269ba2f052a19d)