Coach as a library (#348)

* CoachInterface + tutorial

* Some improvements and typo fixes

* merge tutorial 0 and 4

* typo fix + additional tutorial changes

* tutorial changes

* added reading signals and experiment path argument

rl_coach/environments/gym_environment.py

@@ -30,7 +30,7 @@ except ImportError:
     failed_imports.append("RoboSchool")
 
 try:
-    from rl_coach.gym_extensions.continuous import mujoco
+    from gym_extensions.continuous import mujoco
 except:
     from rl_coach.logger import failed_imports
     failed_imports.append("GymExtensions")