SQLite plugin: store status value in new table

The item status values will be stored in a new table called `status`, which has the same columns as the history table. Additionally it will have a new column `cur`, which contains the current value.

This pull request will also change the behaviour of the `sqlite = init` configuration by requesting the last value from the new `status` table instead from the `history` table (this speed up the initialization phase of smarthome).