Editing table cells, fixes #22

We can edit the cells in the JTable now, and doing so will update the information stored in the ImageObject.

I also made a few tweaks. Resizing the window now gives priority to the additional space to the JTable instead of the DisplayPane. I added columns to the JTable for Date Added and page number. I also tweaked the adjustColumnWidth method of the JTable so now it adjusts the columns to reasonable widths based on the data in the column.