add Remote.readonly

Does nothing yet.

Considered making bup readonly, but while the content can't be removed,
it is able to delete a branch, so didn't.

This commit was supported by the NSF-funded DataLad project.

Remote/Ddar.hs

@@ -78,6 +78,7 @@ gen r u c gc = do
 		, remotetype = remote
 		, availability = if ddarLocal ddarrepo then LocallyAvailable else GloballyAvailable
 		, readonly = False
+		, appendonly = False
 		, mkUnavailable = return Nothing
 		, getInfo = return [("repo", ddarRepoLocation ddarrepo)]
 		, claimUrl = Nothing