Complete backwards incompatible, rework of qc_statem

- Completely remove legacy implementation based on parameterized
  modules.
- Add support for PropEr statem.
- Callback changes
  * Remove scenario_gen/0 and scenario support.
  * Rename command_gen/0 to command/1.
  * Refactor initial_state/1 to take a proplist as 1st argument.
  * Rename setup/0 to init/0.
  * Rename and refactor setup/1 to init/1 to take the initial symbolic
    state as 1st argument.
  * Rename and refactor teardown/2 to stop/2 to take the initial
    symoblic state as 1st argument and the final dynamic state as 2nd
    argument for sequential statem or undefined for parallel statem.
- Deprecate all except the qc_statem_ets demonstration test.
Add initial_state/0 to eqc_statem behaviour
Remove deprecated code
Refresh edocs
Update rebar (2.4.0-3-ga00f8c6)