move files from plugins directory as it seems to be used by new plugin system by Dune (that's weird)

- now properly records the scopes
- only register requested ones

- Renamed type declarations as lustre_types and machine_code_types

- program type renamed as program_t
- Initiating the lustrev tool with dependencies to z3 and seal.

- EMF backend now impose the optimization level to be set to 0 in order to avoid equation elimination that would render traceability difficult
- Options.ml has been split into Options.ml / Options_management.ml. Options.ml only contains references and no functions

- New fonction in plugins: main_loop_body_prefix