The idea behind the new parley practice interface is to present everything
to the user in a more visual way. Objects needed to practice vocabulary
are represented by their real counterparts. For example, the word currently
being practiced, usage examples, and a picture can be compiled on a card,
which shows the close relation of these things. Also a stop watch could be
shown that displays the remaining seconds.

All this information is drawn on the canvas, and the user cannot interact
with it directly. For input, there will be separate widgets at the bottom
of the window.

Here's a list of objects that could be put in the practice window:

VIEW:
o the card with the actual vocabulary information on it
o a stack with the remaining cards - a good way to give the user an idea
  of how much of the vocabulary is left
o an info bar that can give hints
o a pie-chart-like thing that shows the progress
o a dynamic diagram with the statistics of the current practice

INPUT:
o a QLineEdit
o "Hint"
o "Solve"
o "Verify"
o "Skip"
o "Next"
o "Previous"
o "Stop Practice"
o an "Edit" button that could pop up a dialog to modify the current word
  and all its associated properties (in case the user spotted a typo, for
  example)
