[tanglegrams] RHS tree data not added to filter options

[jameshadfield]

Filtering data unique to the RHS tree don't appear in the filter dropdown list, (presumably) due to us not considering the RHS tree when we collect them.

Note that if the filtering options (as set by the LHS tree and therefore in the dropdown) are present on the RHS tree then filtering works as expected.

[jameshadfield]

The fix for this looks relatively straightforward I think. Briefly:

• The <FilterData> component needs tree.totalStateCounts to compute options
• We don't compute this for the second tree upon load (and there are two ways to load a second tree!)
• Computing this on load and passing it to the rendering component should be enough