Implement Admin::BlogPosts #edit and #update actions.

- Current spec status: 147 examples, 0 failures in 1.54 seconds.
Implement Admin::BlogPosts #destroy action.

- Current spec status: 150 examples, 0 failuresin 1.59 seconds.
Add JS confirmation modal for Admin::BlogPosts #delete.

- Current spec status: 150 examples, 0 failures in 1.55 seconds.