Added foundation for exam-form element

Bare minimum implementation as a foundation for the
exam-form element.
Removed unnecessary nested divs
Removed unnecessary core-header-panel attrs
Imported exam-form into main element
Set exam-card background to white
Implemented hero transition for the exam-form
Transferred fabBack inside exam-form element

To make the exam-form look like 1 big card covering the
whole area.
Improved exam-form formatting
Implemented paper-radio-group for question choices
Added paper-button for submitting answers

In the future, this button will be used to submited
the selected choice as the user's answer.
Added prev and next buttons

For the user to move to the previous or next question
relative to the one currently being answered. This is
just the UI for this feature, no functionality yet.
Removed unnecessary console print
Mde paper-fab color attr universally white

All fabs are now have their icons consistently white.
Added hover effect for all fabs
Set paper-element styles to universal

To avoid having to redefine styles per sub-element
and to have a consistent design among all paper elements
used.
Reordered exam-form formatting

Logically ordered css definitions, removed unnecessary
styles, added displaying of current question # and total
# of questions.