Changes

Remove the SubTypeHierarchyCache.

This was used in WOD validation. The problem with WOD validation is that
if it happens before a build, you will get errors about components that
were not found or do not extend WOElement. This cache made that
validation error permanent, requiring a WOLips restart to clear it. And
the validation during build made those errors somewhat random due to the
race condition between build and validate. This led to what was known
lovingly as "the eclipse dance" where you needed to 1) disable automatic
builds 2) clean the project 3) restart eclipse 4) build the project and
5) hope the errors went away or do it again.

The cache doesn't even seem to save any time, but it does cause a lot of
headache, so I'm removing it.
 (commit: 356d8ad)