Added task new_qpost in order to add a new post to the queue file.
Made install task create queue directory
Stopped extraneous mkdir_p when creating posts
Aded optional future date on new_post
Made Octopress not publish future-dated posts.

Used implementation from the following commit:
https://github.com/jbrains/octopress/commit/4b9b499251ea4d613f7bd6f3b0500c6485c5ec21
Made rake preview respect --no-future
Added publish_next task