Add "Toggle spell check for file" command

[cmcginty]

I was looking for a simple way to disable spell check on a single file. So I see there was a toggle feature added for workspaces in #64. I was hoping it would not be too hard to add this for a specific editor tab/file.

For example, let's say I have a very large file that I do not want to spell check, but I don't want to disable all the other file in my workspace.

This would be a useful feature also as I like to have spell check enabled by default, but might want to disable it when I know am hacking on a single file and don't want to be distracted with spelling.

[nvmnghia]

Is there any progress on this?

[sjorspeterse]

I'm also looking for this feature