Add column buttons for sorting courses

[jepoorbaugh]

Users should be able to click a button on the right side of the "# of students" and "# of credits" columns to sort the table by these values in ascending order or descending order so users can quickly discover the most enrolled and least enrolled classes for various filters.

The button should change its icon to show the current sort being performed. For example, an up arrow (↑) could show that the table is being sorted in ascending order, or a down arrow could show it is being sorted in descending order.

[jepoorbaugh]

Here is a picture of how the table should look as a whole