Add "spell" command

[henderea]

In Alfred, there is a spell command that I use a lot, where you type spell word and it gives you spelling correction suggestions on word. Foe example, type spell superflous and it suggests superfluous, which you can copy to the clipboard by actioning it. If there are multiple possibilities, it will list them as separate items. I'm not overly great at spelling, so I use it fairly often in Alfred. You enable it under the dictionary feature settings in Alfred, so I'm assuming it's something available through the macOS dictionary app. It would be really awesome to have this functionality in Lacona, and I don't think it would be overly hard to do if you already have a define command.