odML to graphML converter.

`graphML` [link](https://en.wikipedia.org/wiki/GraphML) is used in graphics community a lot. Here is a simple conversion code that can be used in odML. This would be helpful for importing odML to graph databases natively. Here is an example conversion that can be used as a basic starting point.

```python
"""

odml2graphml

Basic odML to graphML converter

(c) 2017 German Neuroinformatics Node (G-Node)

"""

import xml.etree.ElementTree as ET
from pygraphml import Graph
from pygraphml import GraphMLParser
import uuid

# Files
base_name = 'rg_dummy'
odml_fname = base_name + '.odml'
graphml_fname = base_name + '.graphml'

# Read odml
tree = ET.parse(odml_fname)
root = tree.getroot()

odml_graph = Graph()
child_id = 0
is_terminal_node_prev = False
prev_uuid_value = 0
prev_node = 0
is_odml_rel_node = 0
prev_tag = 'odML
for elem in tree.iter(): # iter over elements
is_terminal_node = elem.getchildren() == []
is_odml_tag = elem.tag in ['section', 'odML', 'property']
if(is_odml_tag):
uuid_value = str(uuid.uuid4()) # generate UUID for an element
node = odml_graph.add_node(uuid_value)
node["odml_entity"] = elem.tag
node["uuid"] = uuid_value
child_id = 1
is_odml_rel_node = 0
if(elem.tag == "odML"):
odml_node = node
else:
node[elem.tag] = elem.text
node["labels"] = ":reach2Grasp"
is_terminal_node_prev = is_terminal_node
if(is_odml_rel_node < 1 and child_id > 0 and is_odml_tag == True and prev_tag in ['section', 'property']):
edge = odml_graph.add_edge(prev_node, node, directed=True)
edge = odml_graph.add_edge(odml_node, node, directed=True)
edge['relation'] = 'child'
if(elem.tag in ['section', 'odML']):
is_odml_rel_node = 1
prev_node = node
prev_uuid_value = uuid_value
prev_tag = elem.tag
parser = GraphMLParser()
parser.write(odml_graph, graphml_fname)

```