Revert "remove class based exercises"

This reverts commit 290e7f1da4.

sumAll/sumAll.js

@@ -1,20 +1,5 @@
-var sumAll = function(a, b) {
-  if (a > b) {
-    let temp = a
-    a = b
-    b = temp
-  }
-  if (
-    a < 0 || b < 0 ||
-    typeof a != 'number' || typeof b != 'number'
-  ) {
-    return 'ERROR'
-  }
-  let sum = 0
-  for(let i = a; i < b + 1; i++) {
-    sum += i
-  }
-  return sum
+var sumAll = function() {
+
 }
 
 module.exports = sumAll