Better compatibility with Solr Search Engine Bundle and support for Trash management

• New: migration step: migration/sleep to delay execution of a migration for a fixed number of seconds

• New: migration steps: location/trash, trash/purge, trash/recover and trash/delete

• Improved: do not use the Repository Search Service when matching Contents or Locations using only their Id or Location Id.
  This has the advantage that those items will always be loaded from the database, even in the case of Solr Search Engine Bundle being enabled, which in turn means that you should get fewer problems related to usage of database transactions and delays Solr in indexation.
  This fixes issue #134.
  BC note: if you use Solr Search Engine Bundle and the find the new behaviour undesireable, you can easily switch back to the previous one by altering the value for parameters ez_migration_bundle.content_matcher.class and ez_migration_bundle.location_matcher.class