[BUG]: sqlite3 schema type for 'timestamp' is 'TEXT' but should be 'DATETIME'

Not a big bug and doesn't affect operation of plugin, but the type of the column `timestamp` in the schema for the `energy_data` sqlite3 database should be `DATETIME` and not `TEXT`

It would be helpful for those (like me) who want to slurp the database into a pivot table to play with it...