Save Blog Posts as Draft and Show List of Drafts

This ticket depends on #409 (closed) and #411 (closed).

There should be a tab "Drafts" that shows all unpublished blog posts. When writing a blog post, add an option to the menu that allows to save the post as a draft. When clicking on a draft post, the normal blog editor (#411 (closed)) should be opened with the post. The draft tab should have an option to start a new post.

mentioned in issue #405 (closed)

@Megalox I was thinking (yes that does happen ): How about we scrape the drafts tab and show drafts instead directly in the blogs listed in the 'My Blogs' tab? They could be shown before the other posts and maybe are greyed out or have a DRAFT tag to be distinguished easily from the rest.

@grote We could do this, but what is the problem with the existing solution and what are the advantages of your proposal?

mentioned in issue #411 (closed)

Problems with extra drafts tab:

• precious horizontal space in tab bar used for drafts
• requires extra blog post list and logic for draft posts
• when users want to publish a post, they see a different screen and need to choose a blog for publication

Advantages of having drafts in My Blogs:

• never more than 4 tabs
• no dedicated blog selection screens (easier to implement)
• blogs posts and drafts for each blogs kept together (wordpress style)
• when users click publish, the post is actually published without needing to make more choices

But both approaches have their pros and cons, so I'm fine with whatever we choose to do.

Milestone removed

Added ~3 and removed ~1 labels

Related to #91 (closed).

Removed ~13 label

mentioned in issue #996

mentioned in issue #895

mentioned in issue #1115

changed the description

added S: stale UI/UX labels

Another user asked for this.