Added trailing slashes

Added trailing slashes otherwise the course_id regex sometimes eats up get parameters.

LMS-2738

Example error:
```
Internal Server Error: /course_modes/choose/BUx/SABR101x/2T2014?upgrade=True
Traceback (most recent call last):
  File "/opt/edx/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 111, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "/opt/edx/local/lib/python2.7/site-packages/newrelic-2.18.1.15/newrelic/hooks/framework_django.py", line 492, in wrapper
    return wrapped(*args, **kwargs)
  File "/opt/edx/local/lib/python2.7/site-packages/django/views/generic/base.py", line 48, in view
    return self.dispatch(request, *args, **kwargs)
  File "/opt/edx/local/lib/python2.7/site-packages/newrelic-2.18.1.15/newrelic/hooks/framework_django.py", line 829, in wrapper
    return wrapped(*args, **kwargs)
  File "/opt/edx/local/lib/python2.7/site-packages/django/views/generic/base.py", line 69, in dispatch
    return handler(request, *args, **kwargs)
  File "/opt/edx/local/lib/python2.7/site-packages/django/utils/decorators.py", line 25, in _wrapper
    return bound_func(*args, **kwargs)
  File "/opt/edx/local/lib/python2.7/site-packages/django/contrib/auth/decorators.py", line 20, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "/opt/edx/local/lib/python2.7/site-packages/django/utils/decorators.py", line 21, in bound_func
    return func(self, *args2, **kwargs2)
  File "/opt/wwc/edx-platform/common/djangoapps/course_modes/views.py", line 54, in get
    course = course_from_id(course_id)
  File "/opt/wwc/edx-platform/common/djangoapps/student/views.py", line 132, in course_from_id
    course_loc = CourseDescriptor.id_to_location(course_id)
  File "/opt/wwc/edx-platform/common/lib/xmodule/xmodule/course_module.py", line 830, in id_to_location
    return Location(course_id_dict)
  File "/opt/wwc/edx-platform/common/lib/xmodule/xmodule/modulestore/__init__.py", line 214, in __new__
    check_dict(kwargs)
  File "/opt/wwc/edx-platform/common/lib/xmodule/xmodule/modulestore/__init__.py", line 179, in check_dict
    check_list(list_)
  File "/opt/wwc/edx-platform/common/lib/xmodule/xmodule/modulestore/__init__.py", line 186, in check_list
    _check_location_part(list_[4], INVALID_CHARS_NAME)
  File "/opt/wwc/edx-platform/common/lib/xmodule/xmodule/modulestore/__init__.py", line 59, in _check_location_part
    raise InvalidLocationError("Invalid characters in {!r}.".format(val))
InvalidLocationError: Invalid characters in u'2T2014?upgrade=True'.
```