Added converters to Model Criteria

If a criteria pushes a filter value to the stack the user given value
is converted according to the filter tag, e.g. text, number, date and
so on
Merge branch 'master' into wobb
Added Purchase which lets you import CSB files

You may now import CSB files for different buyers, create deliverers
and sub-deliveres which are relating to a person entry. Missing persons
will be created. Also added Var stuff to handle variables and fixed
prices.