anova should report omnibus test results

[gregcaporaso]

Improvement Description
It's possible to get significant terms in ANOVA results, but for the model overall to not be statistically significant. If the model itself isn't significant, individually significant terms are likely not informative.

Current Behavior
The statistics for the overall model are not presented to the user in the anova visualization.

Proposed Behavior
The statistics for the overall model should be presented to the user in the anova visualization, at least including the F statistic and the p-value. I think it could make sense to present the full OLS regression result summary (building from this code, that would be lm.summary().