Add standard deviation bars to ground failure plots

[dslosky-usgs]

@kallstadt-usgs

Find the preferred groundfailure/liquifacation model in info.json using:
landslides[#].prefered == true
liquifaction[#].prefered == true

Use 2 standard deviations, which are stored under the properties hagg_2std for hazard and pop_2std for population in the groundfailure/liquification models

[dslosky-usgs]

[dslosky-usgs]

Add "hat" to the triangle so if lower bound is below plot min, we can still show the upper bound without it being awkward