Larger text field for settings values

The `value` field in the settings table was too small for the value inserted when sorting photos by date taken:

```sql
UNIX_TIMESTAMP(STR_TO_DATE(CONCAT(takedate,"-",taketime),"%d.%m.%Y-%H:%i:%S"))
```

The manual migration path for this is running this query:

```sql
ALTER TABLE lychee_settings MODIFY COLUMN `value` VARCHAR(200);
```