Implement string functions

Summary:
Added missing string functions.
I also cleaned up error messages a bit in effort to make them uniform.

Reviewers: teon.banek, buda

Reviewed By: teon.banek

Subscribers: pullbot

Differential Revision: https://phabricator.memgraph.io/D1458

tests/unit/utils_algorithm.cpp

@@ -0,0 +1,22 @@
+#include <list>
+#include <string>
+#include <vector>
+
+#include "gtest/gtest.h"
+
+#include "utils/algorithm.hpp"
+
+using vec = std::vector<std::string>;
+
+using namespace std::string_literals;
+using namespace utils;
+
+
+TEST(Algorithm, Reversed) {
+  EXPECT_EQ(Reversed(""s), ""s);
+  EXPECT_EQ(Reversed("abc"s), "cba"s);
+  EXPECT_EQ(Reversed(std::vector<int>({1, 2, 3, 4})),
+            std::vector<int>({4, 3, 2, 1}));
+  EXPECT_EQ(Reversed(std::list<std::string>({"ab"s, "cd"s})),
+            std::list<std::string>({"cd"s, "ab"s}));
+}