Abstracts and return of static content

* Abstract field was added to projects. It's just a text field at the moment.
* Templates make use of a method which returns either that field or a shortened first paragraph of the project's description
* Vignettes on landing page were removed and replaced with static content in the templates
* landing-page specific styles were removed

CSS classes were chosen with "meh" in mind -- just aiming to get the content present.
We can do that, but it'll require we notify the template that the string has been shorted. Otherwise, there'll be an ellipses on all of the text, which would be misleading. LMK if you think that should be implemented or if this is simpler.