Stack Creation Form on Manage Stacks Page

Added a full-fledged Stack Creation form on the "Manage Stacks" page. Now users can make stacks from either a page by using the Shortcode Button, or on the Manage Stacks Page.
Show "Loading Brick..." until fully loaded

Because we do some re-arranging of the Brick editor upon load, to make it look clean, we will hide all page contents and show a "loading brick editor..." message until it is layed out properly.

Also, the message which lets the user know which brick they are editing below the Brick Title on the Brick Editor page now shows on both Add New and Edit Brick pages.
Fixed new margins for Minimal Admin

For the minimal admin pages, margins have been re-set in wordpress 4.0 and no longer need to be set to 18px. Here I set them to be 0