Allow creating new drafts and saving them

[vickychijwani]

This issue belongs to the create / edit post epic: #5.

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Notes on implementation

Experimentation with the /posts API reveals that it is very forgiving in general :). For example, the following short request will successfully create a new draft (of these parameters, only title and markdown are required):

POST /posts/

Content-Type: application/json; charset=utf-8
Authorization: Bearer <access_token>

{
    "posts": [{
        "title": "(Untitled)",
        "markdown": "",
        "status": "draft"
    }]
}

201 Created

{
    "posts": [{
        "id": 27,
        "uuid": "5f04e432-67e4-48be-a3b8-0a3beb3d5b0c",
        "title": "(Untitled)",
        "slug": "untitled-4",
        "markdown": "",
        "html": "",
        "image": null,
        "featured": false,
        "page": false,
        "status": "draft",
        "language": "en_US",
        "meta_title": null,
        "meta_description": null,
        "created_at": "2015-04-23T02:24:42.553Z",
        "created_by": 1,
        "updated_at": "2015-04-23T02:24:42.553Z",
        "updated_by": 1,
        "published_at": null,
        "published_by": null,
        "tags": [],
        "author": 1,
        "url": "/untitled-4/"
    }]
}

Test cases

• [Online] New draft => back => new post should be at the top and have the status "Draft"
• [Offline] New draft => back => new post should be at the top and have the status "Saved locally"
• [Offline] New draft => back => another new post should be at the top and have the status "Saved locally"
• [Offline] Open any previously-created offline draft => back => nothing should change
• [Offline] Open any previously-created offline draft => save => back => nothing should change
• [Online] Swipe to refresh => status of all local drafts should change to "Draft"