Finish QuizRunner unit testing

for now at least; it’s somewhat frustrating with how minimal the public
interface is
StudentData unit testing

should be complete
also minor changes elsewhere, to the question selection algorithm in
QuizRunner
Added AppButton testing

Should be finished, since AppButton is a simple class
Changes to StudentData testing to fix bugs
Make AppButtons show correctly

Set the text in the constructor and set visibility in layoutButtons
Modify quiz gating in MapPanel

Make it so the user can’t take a quiz if they haven’t seen any
countries in the area to be quizzed upon

Appropriate data fields were added to StudentData and corresponding
tests were added.

Also includes misc. fixes to MapPanel and ContinentData
QuizRunner algorithm fairness changes

QuizRunner should now only ask about countries and continents the
student has actually looked at.
Fix returns types in DataManager

so the casts actually work, which is mildly important
Merge remote-tracking branch 'origin/Lauren' into Adam

Conflicts:
	src/project/DataManager.java
	src/project/MapPanel.java
	src/project/StudentData.java
Delete old images

at least I hope they’re old and unneeded…
Cleanup final merge issues

aka some dependency gunk in WelcomeWindow
MapPanel testing

amusingly enough, we can’t really test MapPanel, since all its methods
are either private or UI related
DataManagerTest created

Also a whole bunch of misc cleanups in other files (mostly removing
stray includes) and some changes to DataManager’s constructor
WelcomeWindowTest etc.

Also includes some minor changes in MapPanel and WelcomeWindow

All testing has now been started with the exception of ContinentData,
which Joe said he would handle IIRC
Refactor ActionListener in WelcomeWindow

the buttons now use the window itself as their ActionListener instead
of each button having their own, saving us some complexity
Revert "Merge branch 'master' into Lauren"

This reverts commit 1cd86c02c52ddd1a9c9e1ee5fc01257399a2735e, reversing
changes made to fb6951e98a049edee8648704fe71d135d0f27071.
Merge remote-tracking branch 'origin/Adam' into Lauren

Conflicts:
	src/project/DataManager.java