Two changes are needed since the unification of the database tables

* When an extension version is uploaded or removed, the *_extension table
needs an update (which was not the case before) with the current version
information.
For this reason the "ExtensionKey" API has a "UpdateExtensionInformation"
method now, and some internal functions are moved to the ExtensionKey class

* When an extension version (or extension) is deleted, Extbase attempted
to also delete the information (which already happened in the TER)

The SolR Re-Indexing is now placed at a more central point.