Fix formatting (unclosed markup), now that we have Scala doc.
Move `getOption` out of `asyncExec`, since this leads to a deadlock.

The deadlock is broken by a timeout after 10 seconds, but the problem remains,
and is especially annoying when waiting for a quick fix.
Cleaned up Scala hovers and moved editor classes in the API packages.
Make sure we are looking at the current contents when computing hovers.
Merge pull request #816 from dragos/api/scala-hover

Scala Hover API and fixes