Revamped so that conversions work for links

The following conversions work :
1. Oriented Gauss code to PD
2. PD to Oriented Gauss code
3. PD to Braid
4. Braid to PD (the last components have to be edited).

So to summarize the work that remains :
1. Braid to PD, correct the last components
2. Gauss code and the DT code have to be edited to work for any input.
3. Rename the methods.
4. Storing.