Figure node

Introduce a new node type "figure".
Management of figures is a boring work.
Figure nodes manage figures as a node in DataProcessor.

User interface will be the following:
```
registerfigure -P /path/to/figure/project fig1.eps fig2.eps
registerfigure -P /path/to/figure/projcet --depends=/path/to/data/dir1,/path/to/data/dir2 fig_summary.eps
```

But it is still under construction.
If you have any ideas, please let me know.