Use tab invisible that is available in Inconsolata

Previously a non-Inconsolata character
was being used which caused alignment issues
with selections and the cursor

Also switch values in editor.coffee to use codes
so they can be viewed in any font.

src/app/editor.coffee

@@ -287,9 +287,9 @@ class Editor extends View
 
   setInvisibles: (@invisibles={}) ->
     _.defaults @invisibles,
-      eol: '¬',
-      space: '•',
-      tab: '▸'
+      eol: '\u00ac',
+      space: '\u2022',
+      tab: '\u00bb'
     @resetDisplay()
 
   checkoutHead: -> @getBuffer().checkoutHead()