remember position and size of developer tools window

it's nice when quitting and relaunching an app a whole bunch during debugging to have things come back up the way you last had it.  this change enables that for a detatched dev tools window on mac.  the downside is multiple dev tools windows will all come back up in the same place, as they will all share the same frameAutosaveName.
Perhaps we should include "brightray" in here somewhere to avoid conflicting with autosave names chosen by the embedding application?