Improve display on mobile devices

[pmolodo]

ie, currently, on my iphone, in portrait mode, the graph is stretched "too" high - looks odd
but in landscape mode, the controls on the left are larger than the max height of the screen; this sets the min size for the entire layout, including the plot to the right, meaning that the plot doesn't fit on the screen

For portrait, need a way to set a max height (or max aspect ratio?)
For landscape, need a way to make the min plot height not tied to the height of the controls on the left. Possibly but enclosing the controls on the left in a scrollable column? Ie, something like what is described here:

bokeh/bokeh#7321
https://groups.google.com/a/continuum.io/d/msg/bokeh/4IfHxkYweV4/yW9GGPbbBAAJ