Implement CDT bulk load method that don't panic if constraints intersect

[Stoeoef]

With the introduction of try_add_constraint and add_constraint_and_split CDTs can finally be created without the risk of panic when built iteratively.

However, the much more efficient bulk loading doesn't support this at the moment.

Spade should implement two new bulk load methods:

• try_bulk_load (name is up for discussion) which skips all conflicting edges. the conflicting edges should be returned.
• bulk_load_and_split (name is up for discussion) which inserts new vertices whenever a conflict arises.