Add tasks table and API

progress will be tracked with this table instead of being in-process
like progress.js

src/routes/backups.js

@@ -2,8 +2,7 @@
 
 exports = module.exports = {
     list: list,
-    startBackup: startBackup,
-    stopBackup: stopBackup
+    startBackup: startBackup
 };
 
 var backupdb = require('../backupdb.js'),
@@ -42,12 +41,3 @@ function startBackup(req, res, next) {
         next(new HttpSuccess(202, {}));
     });
 }
-
-function stopBackup(req, res, next) {
-    backups.stopBackupTask(auditSource(req), function (error) {
-        if (error && error.reason === BackupsError.BAD_STATE) return next(new HttpError(409, error.message));
-        if (error) return next(new HttpError(500, error));
-
-        next(new HttpSuccess(202, {}));
-    });
-}