Show error box when python2.7 is not found

When the plugin is loaded and it cannot find python 2.7, it throws the following error:

Traceback (most recent call last):
  File ".\sublime_plugin.py", line 62, in reload_plugin
  File ".\SublimeYouCompleteMe.py", line 113, in <module>
    SERVER_WRAP = SublimeYouCompleteMe(user_options_store.DefaultOptions())
  File ".\SublimeYouCompleteMe.py", line 55, in __init__
    self._setup_server()
  File ".\SublimeYouCompleteMe.py", line 70, in _setup_server
    command = [utils.path_to_python(),
  File ".\plugin\utils.py", line 88, in path_to_python
    raise RuntimeError("Could not find python 2.7!")
RuntimeError: Could not find python 2.7!

It would be a nice to have to inform the user.