Improve Split to allow split of multiple statements

[vemonet]

At the moment @ammar257ammar needs to repeat the Split step multiple time for Bio2RDF

To Improve this issue we should improve how we provide the statements to be splitted:

• Provide SPARQL select query (@vemonet favourite)
• Provide Triple pattern fragment (@micheldumontier favourite)
• Provide a list of the entity/property to split so that it is done in one shot (@rcelebi favourite)

The 3 are not hard to implement, this is more thinking about the cleanest design for our users that will be the hardest here imho

We could also hit 2 birds with 1 codeblock: allow the user to provide a list of SPARQL queries/Triple Pattern Fragments

Optionally we could allow the user to define the query as a string to avoid the user to create a file when he doesn't need one. But, on the other hand, forcing our users to always define their "split mappings" in a separate file makes it more strict and clearer (which might be less confusing)