store table code refactorization

[zork]

Change store table implementation to allow to:

• express aggregations for SQLArchive backend
• add custom properties for binded members (csv fiels name, xml store-as-attribute/store-as-element, SQL database type)
• set custom order of element storing (for xml backend)
• specify custom primary key instead of hardcoded field named "id"
• allow to use external mappers for class instead of single one.

This ticket blocks #29 and #25. There is a special page StoreTablesAndMappers that describes planned changes in more detail.