Update "Type Hierarchy" automatically when switch file or add "Update" botton

[camacici]

Hi,
initially many thanks for this tool!
It could be usefull show/update the hierarchy every time I switch file or open a new file, so I shouldn't run a search every time.
If it runs down performance it could be usefull add a botton in "Type Hierarchy" that show the hierarchy of the selected class/interface.