started converting to use optparse-applicative

This is a work in progress. It compiles and is able to do basic command
dispatch, including git autocorrection, while using optparse-applicative
for the core commandline parsing.

* Many commands are temporarily disabled before conversion.
* Options are not wired in yet.
* cmdnorepo actions don't work yet.

Also, removed the [Command] list, which was only used in one place.

Command/Migrate.hs

@@ -18,10 +18,10 @@ import qualified Command.ReKey
 import qualified Command.Fsck
 import qualified Annex
 
-cmd :: [Command]
-cmd = [notDirect $ withOptions annexedMatchingOptions $
+cmd :: Command
+cmd = notDirect $ withOptions annexedMatchingOptions $
 	command "migrate" paramPaths seek
-		SectionUtility "switch data to different backend"]
+		SectionUtility "switch data to different backend"
 
 seek :: CommandSeek
 seek = withFilesInGit $ whenAnnexed start