Use zoom instead of font size

[sonulohani]

Hi @ouuan , @coder3101 , @neko-para

Anyway this PR(https://github.com/cpeditor/QCodeEditor/pull/24) got merged but I want to point out that you can't increase font value in floats and what I have seen is that sometimes for small font size like consolas, between pt. 11 and 12 I get my sweet spot at 11.5pt which I can't set it using font settings. That's where zoom comes handy. Its all about providing better user experience.

You can close this issue if you dont agree.