#500 Database update function should update description and category

- Include description and category in update_presentation function

This change is necessary for the new approach to editing talks, which will involve editing a blank talk in the table. Calling this method instead of submit() will prevent the focus on the current talk from being lost.

Fix issue #500
Related to issues #427, #494

Related proposal:
https://docs.google.com/document/d/1VdPLpdIgteMfr1l7TPIZQ1M5XUKcy7ffVWu41t5zvjk/edit#