Adds limit = 0 as a valid parameter for queries (#1493)

* Remove results if limit = 0;

* Adds tests for limit=0 and count=1.

* Improves readability.

src/Routers/ClassesRouter.js

@@ -23,7 +23,7 @@ export class ClassesRouter extends PromiseRouter {
     if (body.skip) {
       options.skip = Number(body.skip);
     }
-    if (body.limit) {
+    if (body.limit || body.limit === 0) {
       options.limit = Number(body.limit);
     } else {
       options.limit = Number(100);