Write LIA doesn't work with SNAP13

[remi-braun]

Subset feature is broken with SNAP13 (see SNAP forum)

This prevent the LIA feature to be used with it.

When new version is release (13.0.1):

• merge the data XMLs
• simplify _get_pp_graph function
• add LIA tests (weekly)

[remi-braun]

Poke @simone-tilia