Timeline now supports linear regressions.

I've added normalization to the way we calculate regressions. This means that our Timeline viz can support linear regressions now and the tooltips will display correctly.

Regressions of other polynomial functions, along with logarithmic and exponential do not play well with Timeline. Until I can create a more permanent solution, I've disabled these regression types on Timeline.

This pull request addresses:

#1299
#1309