Minimal CSV import

[cmoesler]

If we have external data that is not in gradoop format, it is really tedious to get this data into it. For this, it would be nice to have an CSV importer that simply read a csv file of nodes and import them as vertices in the gradoop format and create a graph from it.
After the import, a function to connect the properties of one vertex with properties of another one would be nice as well. With this it is easy for example to mark foreign keys of the data.
It is also useful to create an abstraction of this importer to set a norm for future importer classes like this.
For this I would like to implement this minimal csv importer and the method to connect the properties.