Added feature in Preferences to allow user to chose the font of the page

[jtnguyen45]

Created a drop down of font options that allows the user to chose the type of font used for the app, within the Preferences page. The font changes the entire page automatically when user clicks on a font option. I chose 5 fonts randomly (Arial, Cascadia, Fira Code, Proxima Nova, Verdana) but can change them to different fonts easily if desired.