BREAKING: Change shadow API to return state object

...not entire MQTT message.

Previously GET and UPDATE_ACCEPTED messages would return an object like this:
```json
{
  "state": {
    "reported": { ... },
    "desired": { ... }
  }
}
```

Now they will return an object like this:
```json
{
  "reported": { ... },
  "desired": { ... }
}
```

This is necessary for the upcoming Azure shadow implementation.

Shadow update API is also being changed to take reported state only.

CL: BREAKING: Change shadow API to return state object

PUBLISHED_FROM=8706cfce56532d3f037d9940dbdcec891d43bb0a

include/mgos_shadow.h

@@ -73,8 +73,8 @@ bool mgos_shadow_get(void);
 
 /*
  * Send an update. Format string should define the value of the "state" key,
- * i.e. it should be an object with "reported" and/or "desired" keys, e.g.:
- * `mgos_shadow_updatef("{reported:{foo: %d, bar: %d}}", foo, bar)`.
+ * i.e. it should be an object with an update to the reported state, e.g.:
+ * `mgos_shadow_updatef("{foo: %d, bar: %d}", foo, bar)`.
  * Response will arrive via UPDATE_ACCEPTED or REJECTED topic.
  * If you want the update to be aplied only if a particular version is
  * current,

mjs_fs/api_shadow.js

@@ -37,7 +37,7 @@ let Shadow = {
   // `CONNECTED` event and report the current state, and b) catch `UPDATE_DELTA`
   // event, apply the delta, and report the state. Example:
   // ```javascript
-  // Shadow.update(0, {reported:{temperature: 12.34}});
+  // Shadow.update(0, {temperature: 12.34});
   // ```
   update: function(version, obj) {
     this._upd(version, JSON.stringify(obj));