stat_smooth with method='lm' now supports proper confidence region for se=True

I modified the lm() function in components/smoothers.py

Confidence intervals for OLS fitted values are in statsmodels, but they are buried in a function i'd never used before:

```python
from statsmodels.stats.outliers_influence import summary_table
```

see this answer on stackoverflow for more info:

[confidence and prediction intervals with StatsModels](http://stackoverflow.com/a/17560456/359786)