collorg.communication.* tables now reference collorg.communication.oid_table

A new base_table has been introduced in collorg.communication schema. All
communication object inherit directly or indirectly from this new table.
Some unused tables have been removed from collorg.
* actor.relation
* planning
* i18n
* web.wall
* web.rss
* web.a_rss_topic
* communication.poll

Lost_found.clean method has been impoved. It now uses search to identify the
tuples in which the cog_oid is still present.