Speed up ObjectIndex#add, part one
Speed up ObjectIndex#add, part one

Instead of obtaining the complete class/interface hierarchy for ever
item we add, we can do that once per class; the next time we add an
item of the same class, we'll have the list already.

This shaves off around 10-15% of ImageJ's DefaultCommandService's
initialization.

Signed-off-by: Johannes Schindelin <53fb8db7833fca1e1746dd8592f61048d350f64c@gmx.de>

scijava/scijava-common