New RTGM calculator app

Redo https://earthquake.usgs.gov/designmaps/rtgm/ as an Angular/Plotly app in USGS EHT.

Review existing tool with @bclayton

A later step might include refactoring the new RTGM web service to return the plot data only if one hazard curve is supplied (i.e. when the app is making the call to the web service). These data are really not needed if someone has supplied multiple hazard curves.