TO DO
				    =====
High Priority
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* Load data and generate invoices for specified periods, using a
single file. These features will be addressed after I get 3.1 and
I see if the indexing kit has stabilized...

Low priority
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* Export does not write out expense data... perhaps do it in one file?
* Generate invoices for selected clients only
* Add hours for the day - take care at midnite, etc...
* All the duplicated code for the session and expense lists is
painful. Rethink this.
* Get the column info out of the ColCell class!! Push this logic
back to the Session and Expense classes - get a coldesc table from the
class.