Add ability to add and remove divs.

Will enable adding different plots.
Add dygraph plots to div.

Now there's a self-contained graph in each div.
Add slow_control_time_label, new view.

Returns timestamp as key with all values of slow controls that happen during this time.
Add ability for multiple graphs to be shown.

Also adds support for graphs that don't share all timestamps.
Improve graph visualization, fix some bugs.  

Shows when data is loading, also handles changing plots on the fly.
Remove highlight, seems buggy.