Plotting needs major reworking

This is probably a project for 0.1.3.

Currently, especially with the introduction of iplot, there a is a lot of redundancy in the code. Also, some things take a long time to plot (radial distributions of many cells, storm images with many localizations).

The ideal rework would be something along the lines of cached properties which are derivates from data classes depending on coordinate parameters and plotting parameters. The plot functions can directly access these attributes without any boilerplate.

Example:

```python
def plot_r_dist(data_name='fluorescence', ...):
data_elem = self.cell_obj.data.data_dict[data_name]
ax.plot(data_elem.r_dist) # somehow deal with kwargs
```

Or maybe a new object on ``Cell``, which take ``data`` and has all these properties?