Support for multiple display names in ui.table

[mattrunyon]

As a follow-up to #653, we could support multiple display names for a column and display the longest name that fits in the current width.

A few questions

1. Do we show the column name or display name in the column statistics? Which display name if we use display name?
2. Should copy values unformatted include the actual column name and copy formatted include the currently shown display name?

To implement this we will need to make some adjustments to GridRenderer. Either need to modify drawColumnHeader so it gets info about which column is being drawn (could be breaking). Or we could try adding a 3rd prop like getAllDisplayNames to GridModel.textForColumnHeader and then modify the appropriate places in GridRenderer to pass that prop. We will then need to cache truncation of the names and pick the longest fitting name.