Change engine for storing export user presets

Unit Name: export-user-preset
DB Table: ExportUserPresets
- Id - auto-increment
- PortalUserId
- ItemPrefix - varchar(100)
- PresetName - varchar(255)
- PresetData - text

# Plan

1. create "ExportUserPresets" database table: - 0.2h
- core/install/install_schema.sql
- core/install/remove_schema.sql
- core/install/upgrades.sql
2. create "export-user-preset" unit (no section or templates) - 0.3h
3. in the "\kCatDBItemExportHelper::OnExportBegin" method inside if ( $this->_getExportSavePreset($object) ) { IF: - 0.5h
- lookup user export preset in the database
- if found, then update it with new data (only the "PresetData" column is changed)
- if not found, then create new user export preset
- the "PresetData" column value must be JSON-encoded for easier manipulations by hand
4. in the "\kCatDBItemExportHelper::PrepareExportPresets" method: - 0.5h
- build up array from user-saved export presets
- use the same option key building logic as currently (concatenated list of exported columns)
5. in the "\kDBEventHandler::mapPermissions" method map "OnDeleteExportPreset" event to the "view" permission - 0.5h
6. in the "\CoreUpgrades::Upgrade_5_2_2_B3" method (file: core/install/upgrades.php) add code, that will transform "export_settings" persistent session variable (where export user presets were stored before) into corresponding records in the "ExportUserPresets" database table - 1h
7. confirm, that: - 0.5h
- user export preset removal works for non-root user
- export preset saving/loading works as before (from a user interface perspective)
- export preset data, that was in the database was correctly migrated and can be used
8. review connected task comments & commit