Many issues with handling connections in MSSQL, have rearchitected to
ensure that connections are always opened and closed in a timely fashion
& disposed of cleanly, and removed unnecessary lock statements. SQL
Server performance seems to have improved considerably as a result,
and various timeout errors seem to have been fixed.
* Migration should be automatic on sqlite and mysql
* Migration is not automatic on mssql, you will need to drop the invType column manually
* Migration should be fine, but as for any db change, I would recommend making sure you have backups before moving past this revision
