#31 Review deletion mechanism

[Tim De Pauw]

Rather than physically deleting the records, perhaps it
would be desirable to change the "approved" attribute
of quotes to "status", and use that to store one of
these statuses:

0: unapproved
1: approved
2: deleted

This would make Undo operations possible, and probably
offer a couple more options. The downside would be a
bit of superfluous memory usage, especially if the QDB
got spammed somehow. Perhaps something like a Recycle
Bin would be useful. Needs looking into.