Juicing up XP animations

[wcjord]

When you get XP, the PointsGainedAnimation widget displays them with a " XP" floating up. We can make this more juicy/gameful in a number of ways:

• Have individual green "+" icons float up instead of + XP, with number equal to the total number of XP.
• Include one vocab icon for each new lemma used
• Include one grammar icon for each new morphological concept used

The exact position should be randomly distributed along the x-axis within the bounds of the left and right edge of the message. They should start around the top of the message and float upwards, "swaying" from side-to-side as they rise.

[linhtphung]

I think it would be nice, but I think the + icon and the vocab and grammar icons are currently not that visually appealing. If we can design something more colorful and delightful, it may enhance the experience. For example, the number of xps can be contained in a star or bubble or flower floating up.