[*] metrics(Part 1) Add env-helpers to iso core

Summary:
This is a set of functions which will allow isomorphic-core to detect
which environment it is running on.

This will be useful for moving the metrics reporter to iso-core

Test Plan: manual

Reviewers: mark, spang

Reviewed By: spang

Differential Revision: https://phab.nylas.com/D3966

packages/isomorphic-core/src/env-helpers.es6

@@ -0,0 +1,8 @@
+
+export function isClientEnv() {
+  return typeof window !== 'undefined' && typeof window.NylasEnv !== 'undefined'
+}
+
+export function isCloudEnv() {
+  return !isClientEnv()
+}