[FIX] Api\Droplet:rename require `name` not `image`

https://developers.digitalocean.com/#rename-a-droplet
Add missing #snapshot API.

Add ability to snapshot droplet.
https://developers.digitalocean.com/#snapshot
Fix bug undefined access stdClass.

Fix bug for #16
Add datetime setter.

To convert DateTime to default locale.
Add ability to convert datetime.

Add convert datetime function utility to use in child class.
Add datetime setter.

Add - Droplet#setCreatedAt
Add datetime setter.

Add - Image#setCreatedAt
Update Droplet.php
Merge branch 'master' of https://github.com/liverbool/DigitalOceanV2 into liverbool-master

Conflicts:
	src/Entity/Droplet.php
Merge branch 'liverbool-master'