Ask sqlite to check foreign keys Related to #4846892

Add reference from etype table's eid column to the entities table Related to #4846892.

[server] change order of entities table modification vs entity creation/deletion In order to have a foreign key referencing the entities table, the insertion into entities must happen first, and the deletion must happen last. For the deletion case, this means we need to: 1. delete all relations (cascade) 2. delete the entities themselves 3. delete the corresponding lines from the entities table This means the _delete_info{,_multi} methods can't keep doing 1 and 3. Thankfully the "public" delete_info method appears to be unused, so drop it. Related to #4846892.

Use foreign keys for relations tables Closes #4846892

Add foreign key for inline relations Related to #4846892

Use our version of schema2sql Related to #4846892

Steal schema2sql module from yams It has no user inside yams, and we need it here if we want to be able to reference the (cubicweb-only) entities table from other tables. Related to #4846892

[dataimport] fix pylint detected error in SQLGenObjectStore

[restore/portable] properly restore the numrange generator If the dump format version is 1.1, read and restore numranges. Closes #4870338

[backup/portable] properly write the eid numrange generator (the eid is no more a sequence) Bump format version to 1.1. Related to #4870338