Postgres: Operations, Hooks, OAuth login, Files support (#2528)

* Adds files related tests through fs-adapter with PG

* Schema deletions implementations

* Adds Hooks spec

* Fix test

* Adds support for containsAll (numbers and strings)

* Better support for deleteFields and deleteClass

* Recursive JSON update for authData

* Adds node_modules to travis cache

* Disable temporarily to make tests pass

* Adds _perishable_token support for _User class

* ignore when a table creation fails at init (table exists)

* Adds support for AddUnique and Remove

* PG 9.4 compatible functions

* Re-enable tests

* nit

* Better handling of schema creation race

.istanbul.yml

@@ -1,2 +1,2 @@
 instrumentation:
-  excludes: ["**/spec/**", "**/PostgresStorageAdapter.js"]
+  excludes: ["**/spec/**"]