Complete copyediting of everything

I noticed a few typos in a few random places in XKit today. I know maintaining XKit is a lot of work and typos are unimportant and easy to miss, so I decided to change them myself. I went through every JS file (and a few others) and corrected any typos, inconsistencies, grammatical mistakes, and occasional awkward wording that I found. I did my best not to go overboard with it or change the tone of voice in which anything was written, but if you don't agree with any of my changes, please don't hesitate to undo them!