Review UIs can now be shown inline in a lightbox (i.e. modalBox for now) window rather than having the user render a new page every time. 

To display a review UI as inline, "allow_inline" needs to be set to True in the Review UI subclass (see markdownui.py in the diff for an example). Custom URL patterns can also be defined by a Review UI subclass that can be used in the inline pluggable UI to allow additional custom functionality (such as fetching data through the server using AJAX).

Inline enabled for Markdown Review UI:
- Uploaded a Markdown file with no caption. Clicked "Review". Modal box popped up with filename as title. Displayed the rendered contents of the attachment.
- Uploaded a Markdown file with a caption. Clicked "Review". Modal box popped up with the attachment caption as title. Displayed the rendered contents of the attachment.
- Uploaded a Markdown file with no content. Clicked "Review". Modal box popped up. Displayed empty modal box (since attachment was originally empty).

Inline disabled for Markdown Review UI:
- Uploaded a Markdown file. Clicked "Review". Got redirected to the review UI page; no modal box was shown.

Custom URL pattern initialized in Markdown Review UI:
- Set a custom URL pattern in Markdown Review UI class. Accessing the URL manually (using curl and my browser) loaded the view of that URL pattern, as expected.