ZODB Components: Cache source code in the loader to avoid access to ERP5 Site.

Using DeadlockDebugguer lead to a deadlock when trying to debug a deadlock on
ZODB Component as it was trying to load the Component. Moreover, this required
accessing to ERP5 Site whereas DeadlockDebugguer is used outside.

Steps to reproduce:
  1. Create an Extension Component with a sleep and run it.
  2. Call manage_debug_threads.
ClassTool: Removed in favor of ZODB Components.