HierarchyTable should perform optimised rerendering

[davidje13]

Currently HierarchyTable rerenders its entire content when changed. This should be changed to perform deltas to improve performance:

• each result has an associated row
  • rows need to account for rowspans; maybe group at outermost level
• create any missing row entities and delete extras
  • maybe use 'key' concept from react to reduce rerendering due to reordering
• ensure rows are in correct order in table
  • note that rowspan'd cells will need to be kept on the top-most row of the block
• ensure data in rows is up to date