Add animations tab to emperor

This is still a work in progress and is not ready to get merged, though it outlines the current direction this would take.

I'll mainly outline what's currently possible:

- Select a category in the mapping file by which you want to group your samples i. e. create the trajectory.
- Select a category in the mapping file by which you want to sort the samples in each of the groups, this must be a numeric category a metadata mapping file column where all values are numeric.
- Once these two categories are selected click the play button and see a line begin drawing between the samples in the order that was assigned by the previous two categories.
- Rotate, change colors, zoom in, zoom out, etc the plot as the animation is running (I could not believe it when I saw this :beers: ).

The things that are not possible right now but should be in the near future:

- Select the color of the trajectories, all trajectories are being drawn in white by default right now.
- Pause.
- Speed up or speed down.

----

The backbone for this pull request are two objects `Trajectory` and `AnimationDirector`. These objects take care of the data wrangling within the HTML code, I would appreciate any input on the implementation of these (I still have to update the docs on these, I've used Google's coding guidelines for this).
This block's indentation is odd.