[#9] Set the flash[:info] when rendering unpublished articles
[#9] Render missing article template when access denied.
[#9] flash[:info] messages rendered in the article sidebar.

Includes styling from Twitter bootstrap for alerts. I checked a box
in the custom Bootstrap form for "alerts" and replaced the resulting
bootstrap.css.

Limitations:

Does not include 'close' button to close the flash message.
[#9] Added links in admin panel to preview unpublished articles
[#9] flash[:info] messages on articles can be dismissed.

Rather than include all the button and form styles from Bootstrap, this
just copies over the relevant rules for alert buttons.
[#9] Remove render_markdown check in GuidesController

Guides have always been written in markdown; there is no show_html
template to render.