Introduce type RawIdent; only 9 imports of Data.ByteString.Char8 remain

The fact that identifiers are represented as ByteStrings is now an internal
implentation detail in module GF.Infra.Ident. Conversion between ByteString
and identifiers is only needed in the lexer and the Binary instances.

src/compiler/GF/Grammar/Parser.y

@@ -507,11 +507,11 @@ Patt3
 
 PattAss :: { [(Label,Patt)] }
 PattAss
-  : ListIdent '=' Patt { [(LIdent (ident2bs i),$3) | i <- $1] } 
+  : ListIdent '=' Patt { [(LIdent (ident2raw i),$3) | i <- $1] } 
 
 Label :: { Label }
 Label
-  : Ident       { LIdent (ident2bs $1)   } 
+  : Ident       { LIdent (ident2raw $1)   } 
   | '$' Integer { LVar (fromIntegral $2) }
 
 Sort :: { Ident }