Adding support for changing multiple settings

I like a lighter-weight font on dark themes, so I put together some mods to QuickThemes to allow that. With these changes, the settings file becomes more arbitrary: any Preference can be configured now. 

There is also a new Default.sublime-commands to support super-shift-P.

Despite my expectations, most of this seems to work. Sorry about the many changes; I wasn't thinking about workflow at all.

One problem I just found: in QuickThemes.sublime-settings , in the defaults, I left in a reference to a non-standard color scheme. Not sure how to go back in time and fix that.