Fraction output

[bmg1919]

This may need further testing. All fraction output is mixed if numerator is larger than denominator. I can add an option for improper fractions if desired, maybe even a button to switch the current result from one to the next (mixed/improper, proper, decimal).

[Darkempire78]

Thanks for your PR, here is some changes to do before merging:

• Add an icon to both setting options (the first one is already used by another option)
• When you click on then result, it should display the default result (and vice versa)
• Should not display the fraction output if there is no calculation
• The app crashes when you put a big number like "5555555555555555" (no idea of why)
• Perhaps change the output format to an html format like "^$num/_$deno", because it's very not beautiful right now