Change over from Google Visualize to D3 for Coach Reports

This changes the Scatter view and the Timeline View over from Google Visualize to use D3.

Main changes:
- Timeline data structure now includes "Timescale" which has all the timestamps from each user to set the scale for the timeline view.
- Base Template now imports d3.js

TODO:
- [ ] Clean up cruft from Google Visualizations implementation.
- [ ] Dynamically set the range of the y-axis based on user data. Does not currently do this for timeline view.
- [ ] Clean up y axis options for Timeline view.
- [ ] Create user activity log option for Timeline view.
- [ ] Unhardcode pctmastery as the y-axis value for Timeline view.