Removed jlib; Edited Nav.php Documentation
Clean up Comments and Add Error Handling.

Edited Comments and Added todos for Database.php
    Removed markdown formatting within comments.

Changed the Database.php Constructor
    The Constructor now sets the $table_list property.

Added Exception Handling to Database.php
    The $connect method throws an exception if there is an error connecting to
    the database.

Changed set_selected_table to a private method.

Grouped Public and Private Methods in Database.php
    Public methods listed before private ones.