refactor ExportActions

This will allow disabling exports for remotes that are not configured to
allow them. Also, exportSupported will be useful for the external
special remote to probe.

This commit was supported by the NSF-funded DataLad project

Remote/Web.hs

@@ -10,6 +10,7 @@ module Remote.Web (remote, getWebUrls) where
 import Annex.Common
 import Types.Remote
 import Remote.Helper.Messages
+import Remote.Helper.Export
 import qualified Git
 import qualified Git.Construct
 import Annex.Content
@@ -50,11 +51,7 @@ gen r _ c gc =
 		, lockContent = Nothing
 		, checkPresent = checkKey
 		, checkPresentCheap = False
-		, storeExport = Nothing
-		, retrieveExport = Nothing
-		, removeExport = Nothing
-		, checkPresentExport = Nothing
-		, renameExport = Nothing
+		, exportActions = exportUnsupported
 		, whereisKey = Nothing
 		, remoteFsck = Nothing
 		, repairRepo = Nothing