Errors during save may corrupt a database

[jeroens]

If a database error occurs during an attempt to save a model or scenario, existing rows may be affected to a degree that they are no longer usable for loading. To prevent users from losing work, EwE must have some type of rollback mechanism.

Some research needs to be dedicated whether adodb.net can use proper SQLTransactions for performing rollbacks in case of save errors.

If transactions cannot be used, we may have to build a hokey solution that copies the current .MDB file to a safe location (at either regular intervals or right before any changes are to be made) so we have a way to revert to a working DB.

[jeroens]

Implemented a basic transaction system. Needs further testing!