Fixed parameters for saving All-day events

#### For all_day events the google api v3 requires date parameter 
```javascript
"start": {
  "date": "startDate",
},
"end": {
  "date": "endDate",
},
```
[Google API Reference - All Day] (https://developers.google.com/google-apps/calendar/concepts#all_day_events)

#### whereas for timed events the google api v3 requires dateTime parameter
```javascript
"start": {
  "dateTime": "startTime",
  # Optional
  "timeZone": "America/Los_Angeles"
},
"end": {
  "dateTime": "endTime",
  # Optional
  "timeZone": "America/Los_Angeles"
},
```
[Google API Reference - Timed] (https://developers.google.com/google-apps/calendar/concepts#timed_events)