Pooling inserts to to decrease database transactions

[Muusssi]

The current architecture is far from optimal when it comes to transactions for inserting data to the database. Specifically inserting items such as keywords, tags and log messages could be pooled to far less transactions since they do not require any returned information. Currently each of these items are inserted using individual transactions.

If properly implemented, this would bring considerable performance improvements especially when connection happens over network.

For example pooling insert_or_ignore type transactions could be pooled quite easily without creating big changes to the overall architecture.