Moved font style definition outside of the custom element

Defining it inside the bar-exam-buddy custom element causes
it to not have any effect to the other custom element's shadow
dom. For example, paper-buttons inside paper-dialog do not
inherit the font declared inside bar-exam-buddy.css
Show dialog containing list of questions

When the LIST QUESTIONS button is tapped, a dialog is shown
with all the questions. A temporary hack was used to circumvent
the fact that on-tap doesn't accept any method arguments as of
yet.
Added transition to list questions hover

Also, changed hover cursor to a pointer.
Renamed listQuestions to chooseQuestion

The primary use of this button is for the user to choose
a different question, so this name is more appropriate
chooseQuestion shows "X" icon if wrong

If the user answers a question correctly, chooseQuestion list
displays a check mark. If incorrectly answered, an X mark is
displayed.

Nothing is shown if the user hasn't answered the question yet.
Added icons to correct and wrong toasts
Dynamically change color of icon in dialogListQuestion

Icon's color is set to green if correct, and red if
wrong.