Generate missing row.css from sass file

[przxmek]

This PR fixes the error when running productionized Django with Silk caused by missing css file.

Fix is to generate row.css from row.less file and add it to the repo inside silk/static/ dir.

ValueError: Missing staticfiles manifest entry for 'silk/css/row.css'
  File "django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "django/views/generic/base.py", line 70, in view
    return self.dispatch(request, *args, **kwargs)
  File "django/views/generic/base.py", line 98, in dispatch
    return handler(request, *args, **kwargs)
  File "django/utils/decorators.py", line 43, in _wrapper
    return bound_method(*args, **kwargs)
  File "django/contrib/auth/decorators.py", line 21, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "django/utils/decorators.py", line 43, in _wrapper
    return bound_method(*args, **kwargs)
  File "silk/auth.py", line 31, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "silk/views/requests.py", line 168, in get
    return render(request, 'silk/requests.html', self._create_context(request))
  File "django/shortcuts.py", line 19, in render
    content = loader.render_to_string(template_name, context, request, using=using)
  File "django/template/loader.py", line 62, in render_to_string
    return template.render(context, request)
  File "django/template/backends/django.py", line 61, in render
    return self.template.render(context)
  File "django/template/base.py", line 170, in render
    return self._render(context)
  File "django/template/base.py", line 162, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 938, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 905, in render_annotated
    return self.render(context)
  File "django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "django/template/base.py", line 162, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 938, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 905, in render_annotated
    return self.render(context)
  File "django/template/loader_tags.py", line 150, in render
    return compiled_parent._render(context)
  File "django/template/base.py", line 162, in _render
    return self.nodelist.render(context)
  File "django/template/base.py", line 938, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 905, in render_annotated
    return self.render(context)
  File "django/template/loader_tags.py", line 62, in render
    result = block.nodelist.render(context)
  File "django/template/base.py", line 938, in render
    bit = node.render_annotated(context)
  File "django/template/base.py", line 905, in render_annotated
    return self.render(context)
  File "django/templatetags/static.py", line 106, in render
    url = self.url(context)
  File "django/templatetags/static.py", line 103, in url
    return self.handle_simple(path)
  File "django/templatetags/static.py", line 118, in handle_simple
    return staticfiles_storage.url(path)
  File "django/contrib/staticfiles/storage.py", line 147, in url
    return self._url(self.stored_name, name, force)
  File "django/contrib/staticfiles/storage.py", line 126, in _url
    hashed_name = hashed_name_func(*args)
  File "django/contrib/staticfiles/storage.py", line 417, in stored_name
    raise ValueError("Missing staticfiles manifest entry for '%s'" % clean_name)