WSJT-X Merge Request #11: Fix spelling errors (open)

This MR fixes some spelling errors:

• in one tooltip in widgets/mainwindow.ui

• in some documentation files

• in some comments

I excluded some files and some words from the spell check by running the following command:
codespell --skip=contrib,cty.dat,g4wjs.txt,lib,*qcustomplot*,translations,CALL3.TXT --ignore-words-list=ans,ba,creat,fave,fo,hist,iif,inout,isnt,nd,ons,parm,rcall,sentinal,sur,te --interactive 2 --write-changes