Add "migrate" action ot imapdomo

dotfiles/imapdomo/common.lua

     local valid = {
         newmail = true,
         rewind = true,
-        cleanup = true
+        cleanup = true,
+        migrate = true
     }
     if not valid[action] then
         error("invalid action: " .. action)

dotfiles/imapdomo/utils/imapdomo

     mkusage "newmail" \
             "rewind" \
             "cleanup" \
+            "migrate" \
          -- "newmail - check for and file new mail" \
             "rewind - re-add messages from FILTER_FAIL back" \
             "       to FILTER_QUEUE" \
-            "cleanup - delete or archive old messages"
+            "cleanup - delete or archive old messages" \
+            "migrate - move mail between mailboxes"
 }
 
 mkcmd() {
         *)  break ;;
     esac done
     Action="$1"; shift
-    grep -qw "$Action" <<< "newmail|rewind|cleanup" || usage
+    grep -qw "$Action" <<< "newmail|rewind|cleanup|migrate" || usage
     cmd=$(mkcmd)
     debug -v cmd
     bash -n <<<"$cmd" || die