Nixtool with fixed YAML output & data dump & plot

nix-tool is nearing completion: the YAML output is now correct, you can test it by reading it with python:

```
#!/usr/bin/env python

import yaml
import pprint
import sys

f = open(sys.argv[1])
# use safe_load instead load
yinp = yaml.load(f)
f.close()

pp = pprint.PrettyPrinter(indent=4)
pp.pprint(yinp)
```

Also, there is now a data dump & plot option in the dump module: "--data" and/or "--plot"
To test it run the following commands in the linux terminal:

```
./TestRunner
./nix-tool dump --data --plot test_validate.h5
```

This will automatically generate a `.txt` dump and a `.gnu` plot script _and_  automatically run the scripts for each 2D data array. The first image shows a cool sinus while the next two are just boring "positions" and "extents" arrays.
The dump plot now uses a default plot file if available which makes it possible for the user to set up his own default plot script that is delivered for each data dump with the "--plot" option. If not available it uses an internal default script as before.