Interplot

New chart type added: **bar charts**
* vertical/horizontal
* automatic unpacking of 2D data (Numpy, Pandas, xarray)

**interplot.conf module**
* Modify interplot's presets for automatic generation of plots
* See demo notebook for examples

**Plot.init**
* lazily init a new plot, if one doesn't already exist

new features:

- line / scatter / linescatter modes
- error bars
- proper handling of markers and line_types

Initial release
outsourced the plotting functionality from the toolbox project: https://github.com/janjoch/toolbox