Fixed EZP-18195: $result.object is not correctly created

EZP-18195 duplicates in fact EZP-6838 which has been fixed in an
inappropriate way in cb8ef8f8b66dafbc302fa9c10dae5293b2d95634.

This fix reverts the previous work around. Only relevant columns are
returned and `object remote_id` is returned as `object_remote_id`.

The `remote_id` key still contains the one of the node to ensure BC.

The `eZContentObject` constructor has been revised to additionally
handle information that are frequently given to him and not exploited
especially when created from `eZContentObjectTreeNode`.

This fix improves performance when `remote_id` or content class
information of an `eZContentObject` contained in an
`eZContentObjectTreeNode` are accessed by avoiding additional SQL
queries.

It should also improves the usage of the DBMS query cache mechanism
since fewer columns are retrieved by the modified SQL queries.
Merge pull request #586 from patrickallaert/EZP-18195

Fixed EZP-18195: $result.object is not correctly created