NAWQAAN-206

* Minor cleanup before I add the new plot
* Mostly coming out of canvas research task
Merge pull request #195 from isuftin/master

a -> an
NAWQAAN-206

* Added Flow Duration plot to Hydrograph.js (tied to same data)
* Added Wrapper which constitutes both plots
* Cleaned up a bit of the code surrounding this connection
Merge pull request #196 from isuftin/NAWQAAN-290

Added two linked maps to Mississippi page
Merge pull request #197 from jiwalker-usgs/NAWQAAN-206

NAWQAAN-206
Replaced Mississippi base layers with states layer and great lakes
layer.