Add single query manual test

Summary:
Practical for debugging trivial queries:
```
~ gdb --args ./tests/manual/single_query "RETURN 2 + 1"

Reviewers: mislav.bradac

Reviewed By: mislav.bradac

Differential Revision: https://phabricator.memgraph.io/D1003

tests/manual/single_query.cpp

@@ -0,0 +1,21 @@
+#include "communication/result_stream_faker.hpp"
+#include "database/graph_db.hpp"
+#include "database/graph_db_accessor.hpp"
+#include "query/interpreter.hpp"
+
+int main(int argc, char *argv[]) {
+  gflags::ParseCommandLineFlags(&argc, &argv, true);
+
+  // parse the first cmd line argument as the query
+  if (argc < 2) {
+    std::cout << "Usage: ./single_query 'RETURN \"query here\"'" << std::endl;
+    exit(1);
+  }
+  GraphDb db;
+  GraphDbAccessor dba(db);
+  ResultStreamFaker results;
+  query::Interpreter interpeter;
+  interpeter.Interpret(argv[1], dba, results, {}, false);
+  std::cout << results;
+  return 0;
+}