VIS: added ability to plot DataFrames and Series with errorbars
close #3796

Addresses some of the concerns in issue #3796. New code allows the DataFrame and Series Line plots and Bar plot functions to include errorbars using `xerr` and `yerr` keyword arguments to `DataFrame/Series.plot()`. It supports specifying x and y errorbars as 1. a separate list/numpy/Series, 2. a DataFrame with the same column names as the plotting DataFrame. For example, using method 2 looks like this:

```
df = pd.DataFrame({'x':[1, 2, 3], 'y':[3, 2, 1]})
df_xerr = pd.DataFrame({'x':[0.6, 0.2, 0.3], 'y':[0.4, 0.5, 0.6]})
df_yerr = pd.DataFrame({'x':[0.5, 0.4, 0.6], 'y':[0.3, 0.7, 0.4]})

df.plot(xerr=df_xerr, yerr=df_yerr)
```

This is my first contribution. I tried to follow the contribution guidelines as best I could, but let me know if anything needs work!
