Add a mode to the Periodic Table Quiz to help people associate the elements' names with their respective symbols and vice versa

[HorusGoul]

Depending on the mode, we will display different information as hints (don't confuse with #36):

1. Learn to place elements by their symbol and atomic number. This is the single available mode in the periodic table right now.
2. Place elements by their symbol, name, and atomic number. This would also serve as a review if the person already completed the first mode (1). We would give the user the symbol and then display the names and atomic numbers on the table.
3. Place elements by their symbol, name, and atomic number (Reversed). Same as the second mode (2), but we would give the user the name and then display the symbols and atomic numbers on the table.

We'll probably need to figure out a more intuitive way for users to select the mode. For now, we should add an option to the quiz settings.