Using bitflags for InteractionGroups

[tguichaoua]

I suggest using bitflags for the fields of InteractionGroups.

Using binary representation is error-prone and hard to read (you have to count the number of digit to know wich group is selected). Also bitflags provides methods to manipulate flags and is easy to convert from/to u32

// With u32
InteractionGroup::new(0b0101, 0b0100);

// With bitflags
InteractionGroup::new(Group::Group2 | Group::Group0, Group::Group2);