Improve Fractions with additions, soustractions... Improve
Fraction.toString...Beginning of PolynomePanel (not finished yet).
Correct some problems with CalculMentalPanel (bug when finished one
exercice and typing enter again). Add a minimal size on the windows for
avoid bad view. Must find an answer for how to fix items in the windows.
Merge branch 'master' of https://github.com/gr3gory/GregIsLearningYouMath