more resilient database upgrade and startup

All statements are made resilient to a partially upgraded database.
- CREATE TABLE are done with IF NOT EXISTS
- TRIGGERs are dropped and re-created
- a new stored procedure is added "create_index_if_not_exists"
the procedure check in information_schema if the index exists,
if not does create it
- all INDEXes are created using "create_index_if_not_exists"