New flavor naming conventions

frobboz-mixin
	A flavor which provides the "frobboz" feature when mixed into other flavors.
	This generally has no explicit components, only included-flavors.
	Not instantiatable by itself.

basic-frobboz
	The same as frobboz-mixin except that it alters the "essential character"
	of the window, such that it would not work to mix two of these together
	unless they know about each other.  In certain cases a basic-frobboz
	may be instantiatable without other flavors.

essential-frobboz
essential-frobboz-mixin
	Something which is needed in order to work.  These are often but not
	always components of minimum-window.  They are also usually internal
	things the user does not see.

frobboz
	An instantiatable flavor whose most distinguishing characteristic is
	that it is a "frobboz".


The window flavor is built on a bunch of -mixin's and minimum-window,
which is built on a bunch of essential-'s including essential-window.
essential-window is built on sheet.