adds Modes module

src/Modes.elm

@@ -0,0 +1,16 @@
+module Modes exposing (..)
+
+type ViewMode
+    = Sell
+    | Buy
+    | Grab
+    | Add
+
+
+canSelectIn : ViewMode -> Bool
+canSelectIn mode =
+    case mode of
+        Sell -> True
+        Buy -> True
+        Grab -> True
+        Add -> False