Renaming SourceGrammar to Grammar and similarly for some related types

Included renamings:

	SourceGrammar -> Grammar
	SourceModule -> Module
	SourceModInfo -> ModuleInfo
	emptySourceGrammar -> emptyGrammar

Also introduces a type synonym (which might be good to turn into a newtype):

	type ModuleName = Ident

The reason is to make types like the following more self documenting:

	type Module = (ModuleName,ModuleInfo)
	type QIdent = (ModuleName,Ident)

src/compiler/GF/Infra/Location.hs

@@ -1,6 +1,9 @@
+-- | Source locations
 module GF.Infra.Location where
 import GF.Text.Pretty
 
+-- ** Source locations
+
 class HasSourcePath a where sourcePath :: a -> FilePath
 
 data Location