displaying generic objects

Add 17 fake objects to objects[], one for each object class.  All
specific color as gray.  They're grouped at the start--actually near
the start since "strange object" is still objects[0]--rather than
being among the objects for each class.  init_object() knows to start
at [MAXOCLASSES] instead of [0]; other code that loops through every
object might need adjusting.

For potions, non-stone gems, and non-novel/non-Book_of_the_Dead
spellbooks that don't have obj->dknown set, display the corresponding
generic object rather the object itself.  Fixes the longstanding bug
of seeing color for not-yet-seen objects whose primary distinguishing
characteristic is their color.  Walking next to a generic object
while able to see its spot will set dknown and redraw as specific.
It's slightly disconcerting to have objects change as you reach them;
I hope it's just a matter of becoming used to that.  (If there is any
code still changing the hero's location manually instead of using
u_on_newpos(), it should be changed to use that routine.)

Most of the new tiles are just a big rendering of punctuation
characters.  The potion, gem, and spellbook ones could be cloned from
a specific object in their class and then have the color removed.  I
started out that way but wasn't happy with the result.  I'm not
artisticly inclined; hopefully someone else will do better.  Each of
them is preceded by a comment beginning with "#_"; the underscore
isn't required, just being used to make the comments stand out a bit.

Invalidates existing save and bones files.

doc/fixes3-7-0.txt

@@ -1082,6 +1082,8 @@ when identifying items via menu and more than one pass is needed (so when
 	identifying 3 items and player only picks 1, for instance), issue
 	--More-- because the next menu might cover up the ID message(s)
 slightly more interesting Gehennom filler levels
+don't reveal color of potions, gems, or spellbooks that haven't been seen up
+	close (seeing faraway monster operate on an object counts as up close)
 
 
 Fixes to 3.7.0-x Problems that Were Exposed Via git Repository