Merge #698

698: Split interface into multiple files r=Dirbaio a=thvdveld

Currently, `src/iface/interface.rs` is 5178 lines. I started splitting the interface because I think it was becoming to big when working on RPL. I think splitting it the way I did is currently most logical, however, I'm sure I missed some things. What do you all think?

Co-authored-by: Thibaut Vandervelden <thvdveld@vub.be>

Author: bors[bot]